added explanation for answer

Author: RaeesStevens

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

@@ -11,3 +11,4 @@ const last4Digits = `${cardNumber}`.slice(-4);
 // Card Number is declared as a number and not a string, so slice won't work.
 console.log(last4Digits);
 // Yes this is what I predicted. The error is - cardNumber.slice is not a function.
+// I used a template literal because it will automatically convert the number to a string before slicing.