So we wan't to know from which number can we take 15% and get 75. Well, lets turn that into an equation. Lets say that x is the number we are looking for. So, 15% of x is equal 75 or mathematically: 15% x = 75. Now: (15/100)x=75 and when we multiply both sides with 100 and divide both sides with 15 we get: x=(75*100)/15 and that is equal to: x=500. So 15% out of 500 is 75.