Fix: add error explanations and correct function call count

Author: Samual-Hu

Sprint-1/2-mandatory-errors/0.js

@@ -1,2 +1,7 @@
 //This is just an instruction for the first activity - but it is just for human consumption
-//We don't want the computer to run these 2 lines - how can we solve this problem?
+//We don't want the computer to run these 2 lines - how can we solve this problem?
+
+// Explanation: 
+// Running this without comments gives a "SyntaxError". 
+// This occurs because the computer tries to read plain English sentences as JavaScript code, which it cannot understand. 
+// Adding '//' turns them into comments that the computer ignores.

Sprint-1/2-mandatory-errors/1.js

@@ -2,3 +2,7 @@
 
 let age = 33;
 age = age + 1;
+
+// Explanation: 
+// The error is "TypeError: Assignment to constant variable." 
+// This occurs because we used 'const' to declare the 'age' variable. 'const' creates a constant whose value cannot be reassigned after its initial creation.

Sprint-1/2-mandatory-errors/2.js

@@ -3,3 +3,6 @@
 const cityOfBirth = "Bolton";
 console.log(`I was born in ${cityOfBirth}`);
 
+// Explanation: 
+// The error is "ReferenceError: Cannot access 'cityOfBirth' before initialization."
+// JavaScript executes code from top to bottom. We tried to print 'cityOfBirth' before we actually declared and initialized it on the next line.

Sprint-1/2-mandatory-errors/3.js

@@ -7,3 +7,7 @@ console.log(last4Digits);
 // Then run the code and see what error it gives.
 // Consider: Why does it give this error? Is this what I predicted? If not, what's different?
 // Then try updating the expression last4Digits is assigned to, in order to get the correct value
+
+// Explanation: 
+// The error is "TypeError: cardNumber.slice is not a function."
+// This occurs because the original cardNumber was a Number type. The '.slice()' method only works on Strings and Arrays, not on pure numbers.

Sprint-1/2-mandatory-errors/4.js

@@ -2,4 +2,8 @@ const time12Hour = "20:53";
 const time24Hour = "08:53";
 
 console.log(time12Hour);
-console.log(time24Hour);
+console.log(time24Hour);
+
+// Explanation: 
+// The error is a "SyntaxError". 
+// This occurs because it violates JavaScript naming conventions: variable names cannot start with a number.

Sprint-1/3-mandatory-interpret/1-percentage-change.js

@@ -12,7 +12,7 @@ console.log(`The percentage change is ${percentageChange}`);
 // Read the code and then answer the questions below
 
 // a) How many function calls are there in this file? Write down all the lines where a function call is made
-// Answer: There are 5 function calls in total. They are located on lines 4, 5, and 10.
+// Answer: There are 2 function calls in total. They are both `Number()` and are located on lines 4 and 5.
 // b) Run the code and identify the line where the error is coming from - why is this error occurring? How can you fix this problem?
 // Answer: The error comes from line 5. It occurs because we are trying to reassign a value to `priceAfterOneYear`, which was originally declared as a `const`. To fix it, change `const` to `let` on line 2.
 // c) Identify all the lines that are variable reassignment statements