diff --git a/Sprint-3/1-key-errors/0.js b/Sprint-3/1-key-errors/0.js
index 653d6f5a0..29ce9f80c 100644
--- a/Sprint-3/1-key-errors/0.js
+++ b/Sprint-3/1-key-errors/0.js
@@ -1,13 +1,29 @@
 // Predict and explain first...
 //  =============> write your prediction here
+// Prediction
+// A SyntaxError is thrown with message: Identifier 'str' has already been declared
 
 // call the function capitalise with a string input
 // interpret the error message and figure out why an error is occurring
+// Error message interpreted ====> The error message simply means the name 'str' was declared twice in the same scope
 
-function capitalise(str) {
-  let str = `${str[0].toUpperCase()}${str.slice(1)}`;
-  return str;
-}
-
+// function capitalise(str) {
+//   let str = `${str[0].toUpperCase()}${str.slice(1)}`;
+//   return str;
+// }
+// capitalise("moses");
 // =============> write your explanation here
+// The error here is because the parameter 'str' and the variable 'let str' share the same name in he same scope, thus the SyntaxError.
+// To fix this error, I could either give the variable a different name or reassign the parameter 'str' without 'let', since no new declaration is made
+
 // =============> write your new code here
+// function capitalise(str) {
+//   let capitalised = `${str[0].toUpperCase()}${str.slice(1)}`;
+//   return capitalised;
+// }
+// console.log(capitalise("moses"));
+// |
+function capitalise(str) {
+  return `${str[0].toUpperCase()}${str.slice(1)}`;
+}
+console.log(capitalise("moses"));
\ No newline at end of file
diff --git a/Sprint-3/1-key-errors/1.js b/Sprint-3/1-key-errors/1.js
index f2d56151f..454384a8c 100644
--- a/Sprint-3/1-key-errors/1.js
+++ b/Sprint-3/1-key-errors/1.js
@@ -1,20 +1,32 @@
 // Predict and explain first...
+// My prediction is the program would throw a SyntaxError, because 'decimalNumber' has already been declared as a parameter and also has been declared as a new variable in the same scope
 
 // Why will an error occur when this program runs?
 // =============> write your prediction here
+//An error will occur because 'const decimalNumber = 0.5' clashes with the parameter of the same name. 
 
 // Try playing computer with the example to work out what is going on
 
-function convertToPercentage(decimalNumber) {
-  const decimalNumber = 0.5;
-  const percentage = `${decimalNumber * 100}%`;
+// function convertToPercentage(decimalNumber) {
+//   // The parameter 'decimalNumber' is created as a variable inside the function's scope.
+//   const decimalNumber = 0.5;
+//   // tries to declare new variable called 'decimalNumber' in the same scope, where one already exists as a parameter
+//   // cannot declare same name twice in one scope with 'const'
+//   const percentage = `${decimalNumber * 100}%`;
 
-  return percentage;
-}
-
-console.log(decimalNumber);
+//   return percentage;
+// }
+// // As a result of the conflict nothing runs.
+// console.log(decimalNumber);
+// // This line is outside the function and would not parse, as 'decimalNumber' only exists inside 'convertToPercentage' as a parameter.
 
 // =============> write your explanation here
+// Parameters and variables declared inside a function cannot be accessed outside it.
 
 // Finally, correct the code to fix the problem
 // =============> write your new code here
+function convertToPercentage(decimalNumber){
+  return `${decimalNumber * 100}%`;
+   
+}
+console.log(convertToPercentage(0.5));
\ No newline at end of file
diff --git a/Sprint-3/1-key-errors/2.js b/Sprint-3/1-key-errors/2.js
index aad57f7cf..4e0a059c3 100644
--- a/Sprint-3/1-key-errors/2.js
+++ b/Sprint-3/1-key-errors/2.js
@@ -1,20 +1,28 @@
 
 // Predict and explain first BEFORE you run any code...
-
+// The parameter is written as a value instead of a variable name
 // this function should square any number but instead we're going to get an error
 
 // =============> write your prediction of the error here
+// The program will throw a SyntaxError 
 
-function square(3) {
-    return num * num;
-}
+// function square(3) {
+//     return num * num;
+// }
 
 // =============> write the error message here
+// SyntaxError: Unexpected number
 
 // =============> explain this error message here
+// In the 'function square(3)' JavaScript parser expected a valid parameter name it could use as a variable
+// Since '3' is a number literal, not a valid identifier, the parser cannot understand it and throws a syntax error.
 
 // Finally, correct the code to fix the problem
 
 // =============> write your new code here
+function square(number){
+    return number * number;
+}
+console.log(square(77));
 
 
diff --git a/Sprint-3/2-mandatory-debug/0.js b/Sprint-3/2-mandatory-debug/0.js
index b27511b41..91cc921ba 100644
--- a/Sprint-3/2-mandatory-debug/0.js
+++ b/Sprint-3/2-mandatory-debug/0.js
@@ -1,14 +1,26 @@
 // Predict and explain first...
 
 // =============> write your prediction here
+// My prediction is '320' would be printed first followed by "The result of multiplying 10 and 32 is undefined"
+// This occurs because 'multiply()' does not return anything
 
-function multiply(a, b) {
-  console.log(a * b);
-}
+// function multiply(a, b) {
+//   console.log(a * b);
+// }
 
-console.log(`The result of multiplying 10 and 32 is ${multiply(10, 32)}`);
+// console.log(`The result of multiplying 10 and 32 is ${multiply(10, 32)}`);
 
 // =============> write your explanation here
+// The template literal calls 'multiply(10, 32) to build the string
+// Inside multiply, 'console.log(a * b)' runs immediately, printing '320'
+// This happens before the outer 'console.log' line finishes, because JavaScript has to evaluate 'multiply(10, 32)' first to know what to put in the template
+// 'multiply's' function body only contains a 'console.log' statement without a 'return' keyword
+// A function with no explicit return statement returns 'undefined' by default.
 
 // Finally, correct the code to fix the problem
 //  =============> write your new code here
+function multiply(a, b){
+  return a * b;
+}
+
+console.log(`The result of multiplying 10 and 32 is ${multiply(10, 32)}`);
diff --git a/Sprint-3/2-mandatory-debug/1.js b/Sprint-3/2-mandatory-debug/1.js
index 37cedfbcf..38429c167 100644
--- a/Sprint-3/2-mandatory-debug/1.js
+++ b/Sprint-3/2-mandatory-debug/1.js
@@ -1,13 +1,23 @@
 // Predict and explain first...
 //  =============> write your prediction here
+// The code seems like it would log 'The sum of 10 and 32 is 42' since function 'sum(10, 32)' seems to add two numbers 
 
-function sum(a, b) {
-  return;
-  a + b;
-}
 
-console.log(`The sum of 10 and 32 is ${sum(10, 32)}`);
+// function sum(a, b) {
+//   return;
+//   a + b;
+// }
+
+// console.log(`The sum of 10 and 32 is ${sum(10, 32)}`);
 
 // =============> write your explanation here
+// When the code was run it logged 'The sum of 10 and 32 is undefined'
+// The bug is in line 7
+// 'return' is automatically assigned a semi-colon if it is followed by a line break, making line 8 unreachable
+
 // Finally, correct the code to fix the problem
 //  =============> write your new code here
+function sum(a, b){
+  return a + b;
+}
+console.log (`The sum of 10 and 32 is ${sum(10, 32)}`);
diff --git a/Sprint-3/2-mandatory-debug/2.js b/Sprint-3/2-mandatory-debug/2.js
index 57d3f5dc3..32508566c 100644
--- a/Sprint-3/2-mandatory-debug/2.js
+++ b/Sprint-3/2-mandatory-debug/2.js
@@ -2,23 +2,39 @@
 
 // Predict the output of the following code:
 // =============> Write your prediction here
+// I predict the output would print the last digits of '42', '105', and '806' because the function name is 'getLastDigit' and it's been called by the input values as arguments
 
-const num = 103;
+// const num = 103;
 
-function getLastDigit() {
-  return num.toString().slice(-1);
-}
+// function getLastDigit() {
+//   return num.toString().slice(-1);
+// }
 
-console.log(`The last digit of 42 is ${getLastDigit(42)}`);
-console.log(`The last digit of 105 is ${getLastDigit(105)}`);
-console.log(`The last digit of 806 is ${getLastDigit(806)}`);
+// console.log(`The last digit of 42 is ${getLastDigit(42)}`);
+// console.log(`The last digit of 105 is ${getLastDigit(105)}`);
+// console.log(`The last digit of 806 is ${getLastDigit(806)}`);
 
 // Now run the code and compare the output to your prediction
 // =============> write the output here
+// The last digit of 42 is 3
+// The last digit of 105 is 3
+// The last digit of 806 is 3
+
 // Explain why the output is the way it is
 // =============> write your explanation here
+// The bug is in line 9, where 'getLastDigit()' is declared with no parameters
+// Instead the function body reaches out to 'const num = 103' and disregards the values passed because the function does not declare any parameter 
+
 // Finally, correct the code to fix the problem
 // =============> write your new code here
+// const num = 103 ---- becomes irrelevant 
+function getLastDigit(n){
+  return n.toString().slice(-1)
+}
+console.log(`The last digit of 42 is ${getLastDigit(42)}`);
+console.log(`The last digit of 105 is ${getLastDigit(105)}`);
+console.log(`The last digit of 806 is ${getLastDigit(806)}`);
+
 
 // This program should tell the user the last digit of each number.
 // Explain why getLastDigit is not working properly - correct the problem
diff --git a/Sprint-3/3-mandatory-implement/1-bmi.js b/Sprint-3/3-mandatory-implement/1-bmi.js
index 58b1085f1..2fff81b87 100644
--- a/Sprint-3/3-mandatory-implement/1-bmi.js
+++ b/Sprint-3/3-mandatory-implement/1-bmi.js
@@ -15,5 +15,17 @@
 // It should return a string of their Body Mass Index to 1 decimal place
 
 function calculateBMI(weight, height) {
+  if (!height || height <= 0){ // to catch cases of undefined and null
+    throw new Error('Height must be greater than 0');
+  }
+  const heightSquared = height ** 2;
+  return weight / heightSquared;
+  }
+function formatBMI(bmi){
+  return bmi.toFixed(1); // rounds 'bmi' to 1 decimal place and converts to a string
   // return the BMI of someone based off their weight and height
-}
+        }
+
+const bmiFurMath = calculateBMI(70, 1.73) + 7;
+const displayBMI = formatBMI(bmiFurMath);
+console.log(`The Body Mass Index is: ${displayBMI}`);
diff --git a/Sprint-3/3-mandatory-implement/2-cases.js b/Sprint-3/3-mandatory-implement/2-cases.js
index 5b0ef77ad..9be764f82 100644
--- a/Sprint-3/3-mandatory-implement/2-cases.js
+++ b/Sprint-3/3-mandatory-implement/2-cases.js
@@ -14,3 +14,11 @@
 // You will need to come up with an appropriate name for the function
 // Use the MDN string documentation to help you find a solution
 // This might help https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/toUpperCase
+
+function toUpperSnakeCase(input){
+    if (typeof input !== "string"){
+        throw new Error("Input must be a string")
+    }
+    return input.trim().replaceAll(/\s+/g, "_").toUpperCase();
+}
+console.log (toUpperSnakeCase("lord of the rings season 1 episode 1"));
diff --git a/Sprint-3/3-mandatory-implement/3-to-pounds.js b/Sprint-3/3-mandatory-implement/3-to-pounds.js
index 10754da73..80681a68b 100644
--- a/Sprint-3/3-mandatory-implement/3-to-pounds.js
+++ b/Sprint-3/3-mandatory-implement/3-to-pounds.js
@@ -4,3 +4,24 @@
 // You will need to declare a function called toPounds with an appropriately named parameter.
 
 // You should call this function a number of times to check it works for different inputs
+
+function toPounds(penceString){
+    let cleanNum = penceString.trim();
+    if (cleanNum.toLowerCase().endsWith("p")){
+        cleanNum = cleanNum.substring(0, cleanNum.length - 1);
+    }
+    const paddedPenceNumberString = cleanNum.padStart(3, "0");
+    const pounds = paddedPenceNumberString.substring(0, paddedPenceNumberString.length - 2);
+    const pence = paddedPenceNumberString.substring(paddedPenceNumberString.length - 2).padEnd(2, "0");
+
+    return `£${pounds}.${pence}`;
+}
+
+console.log(toPounds("77770p"));
+console.log(toPounds("2570p"));
+console.log(toPounds("399p"));
+console.log(toPounds("77p"));
+console.log(toPounds("0p"));
+console.log(toPounds(" 50p "));
+console.log(toPounds("777"));
+console.log(toPounds(""));
diff --git a/Sprint-3/4-mandatory-interpret/time-format.js b/Sprint-3/4-mandatory-interpret/time-format.js
index c0dd9c9a5..593439cb3 100644
--- a/Sprint-3/4-mandatory-interpret/time-format.js
+++ b/Sprint-3/4-mandatory-interpret/time-format.js
@@ -1,8 +1,24 @@
+// let padCalls = 0;
+// let padCallCount = 0;
+// let firstNum;
+// let lastNum;
+let lastReturn;
+
 function pad(num) {
+  // padCalls++;
+  // padCallCount++;
+  // if (padCallCount === 1){
+  //   firstNum = num;
+  // }
+  // lastNum = num;
   let numString = num.toString();
   while (numString.length < 2) {
     numString = "0" + numString;
   }
+    //  if (padCallCount === 1){
+    //   firstReturn = numString;
+    //  }
+    lastReturn = numString;
   return numString;
 }
 
@@ -14,6 +30,13 @@ function formatTimeDisplay(seconds) {
 
   return `${pad(totalHours)}:${pad(remainingMinutes)}:${pad(remainingSeconds)}`;
 }
+// for (const s of [8784, 77, 77777]){
+//   padCalls = 0;
+//   const result = formatTimeDisplay(s);
+//   console.log(`formatTimeDisplay(${s})==> ${result}| pad called ${padCalls} times `);
+// }
+formatTimeDisplay(61);
+console.log("The return value of pad when it is called for the last time is:", lastReturn);
 
 // You will need to play computer with this example - use the Python Visualiser https://pythontutor.com/visualize.html#mode=edit
 // to help you answer these questions
@@ -22,17 +45,28 @@ function formatTimeDisplay(seconds) {
 
 // a) When formatTimeDisplay is called how many times will pad be called?
 // =============> write your answer here
+// The 'pad' function is called "three times" within the 'formatTimeDisplay' function
+// The count will always be three because the 'return' statement contains three 'pad()' calls 
 
 // Call formatTimeDisplay with an input of 61, now answer the following:
 
 // b) What is the value assigned to num when pad is called for the first time?
 // =============> write your answer here
+// for the first call to pad, num is assigned the value of 'totalHours', which is '0'
+// Since the template literal is evaluated from left to right, calling 'formatTimeDisplay(61)', the calls occur in this order:
+// totalHours, remainingMinutes, and remainingSeconds
 
 // c) What is the return value of pad when it is called for the first time?
 // =============> write your answer here
+// For the first call to 'pad', 'num' is '0'
+// The pad function will return '00' because it pads single-digit numbers with a leading zero
 
 // d) What is the value assigned to num when pad is called for the last time in this program?  Explain your answer
 // =============> write your answer here
+// The last call is 'pad(remainingSeconds)' which is '61 % 60'
+// since 61 divided by 60 leaves a remainder of 1, it means the value '1' is assigned to 'num' in the last call of pad
 
 // e) What is the return value of pad when it is called for the last time in this program?  Explain your answer
 // =============> write your answer here
+// The return value of pad when called for the last time is '01'
+// since '1.toString()' is '1', the 'while' loop runs once and adds a '0' to the front, giving '01'
diff --git a/Sprint-3/5-stretch-extend/format-time.js b/Sprint-3/5-stretch-extend/format-time.js
index 32a32e66b..62ba5f547 100644
--- a/Sprint-3/5-stretch-extend/format-time.js
+++ b/Sprint-3/5-stretch-extend/format-time.js
@@ -2,7 +2,7 @@
 // Make sure to do the prep before you do the coursework
 // Your task is to write tests for as many different groups of input data or edge cases as you can, and fix any bugs you find.
 
-function formatAs12HourClock(time) {
+/*function formatAs12HourClock(time) {
   const hours = Number(time.slice(0, 2));
   if (hours > 12) {
     return `${hours - 12}:00 pm`;
@@ -22,4 +22,74 @@ const targetOutput2 = "11:00 pm";
 console.assert(
   currentOutput2 === targetOutput2,
   `current output: ${currentOutput2}, target output: ${targetOutput2}`
-);
+);*/
+
+function formatAs12HourClock(time){
+  if (typeof time != "string"){
+    throw new Error (`Expected a string in "HH:MM" format, got ${typeof time}`);
+  }
+  const match = /^([01]\d|2[0-3]):([0-5]\d)$/.exec(time);
+  if(!match){
+    throw new RangeError(`Invalid time "${time}": expected 24-hour "HH:MM" (00:00 to 23:59)`);
+  }
+
+  const hours = Number(match[1]);
+  const minutes = match[2];
+  const period = hours < 12 ? "am" : "pm";
+  const hours12 = hours % 12 === 0 ? 12 : hours % 12;
+
+  return `${String(hours12).padStart(2, "0")}:${minutes} ${period}`;
+}
+console.log(formatAs12HourClock("23:00"))
+
+function check(input, targetOutput){
+  const currentOutput = formatAs12HourClock(input);
+  console.assert(currentOutput === targetOutput, `input: ${input}. current output: ${currentOutput}, target output: ${targetOutput}`);
+}
+
+function checkThrows(input){
+  let threw = false;
+  try{
+    formatAs12HourClock(input);
+  }
+  catch(error){
+    threw = true;
+  }
+  console.assert(threw, `input: ${String(input)} should have thrown an error`);
+}
+
+// original tests
+check("08:00", "08:00am");
+check("23:00", "11:00pm");
+
+// midnight hours
+check("00:00", "12:00am");
+check("00:30", "12:30am");
+check("00:59", "12:59am");
+
+// mornings
+check("01:00", "01:00am");
+check("09:59", "09:59am");
+check("10:05", "10:05am");
+check("11:59", "11:59am");
+
+// noon 
+check("12:00", "12:00pm");
+check("12:01", "12:01pm");
+check("12:30", "12:30pm");
+check("12:59", "12:59pm");
+
+// mid-day and evenings
+check("13:00", "01:00pm");
+check("17:45", "05:45pm");
+check("22:10", "10:10pm");
+check("23:45", "11:45pm");
+check("23:59", "11:59pm");
+
+// invalid times
+checkThrows("24:00", "25:00", "12:60", "99:99", undefined, null, 800, ["08:00"]);
+
+// bad formatting
+checkThrows("", "abc", "8:00", "0800", "08:00:00", " 08:00", "08:00 am");
+
+console.log("Complete! No errors.");
\ No newline at end of file