The question asks me to increase 540 by 15% how do I do that

There's a few ways to do it. First you can take 15% and then add it on to 540:

15% = 15/100 = 3/20

Divide 540 by 20 = 27

Then multiply 27 by 3 = 81

540 + 81 = 621

OR

There's a quicker way where you can just multiply 540 by 1.15 to get 621.

The way to think about it is if you're increasing, you always multiply it by 1. (%)