Pls i don't understand how the answer of the question is 4?

Question

var b=5;
var a=20;
a++; a--;
var c =b % a;
alert (c);

Answer 1

var b=5;
var a=20;
a++; b--; // a = 21, b = 4
var c =b % a; // c = 4 % 21
alert (c); // 4

4 % 21 (modulo division):
21 goes into 4 0 times, there will be a remainder of 4

Answer 2

It isn't?!
The answer of this will be 5...
5%20=5
It can be 4 if you do b-- instead of a--

Answer 3

Definitely 5
Check it for yourself

https://code.sololearn.com/WBvF8m20vt3J/?ref=app

Answer 4

Oh, i am sorry for the mistake, in place of a--, it is b--

Answer 5

Thanks, gotten

Answer 6

I ran it in my text editor and the answer is 4

Answer 7

Pls can u explain the process