Answer 1

"20%" would be a string, you would need to convert it to a numeric type to do calculations with it

Answer 2

1.If you want to get output without using html go for alert();

2.while taking input it is string by default so use parseInt(); to convert to int

3.tip calculation : put 100 in denominator

/*
let bill = parseInt(prompt("What's Your Bill?"));
let tip = (bill * whatTip)/100;
*/

hope this helps!

Answer 3

let whatTip = prompt("What Type Of Tip Are You Looking for? 15% or 20%");
let bill = parseInt(prompt("What's Your Bill?"));
if(whatTip === "20%") {
let tip = (bill * 20)/100;
alert("Your Tip is: "+ tip);
bill=bill+tip;
alert("You New Total is: "+ bill);
}
else if(whatTip == "15%") {
let tip = (bill * 15)/100;
alert("Your Tip is: "+ tip);
bill=bill+tip;
alert("You New Total is: "+ bill);
}

//Is this how you want it to work just check once in playground