To reverse a percentage decrease you divide it by the decrease (+ 100%)
For example we will pick the number, 100, which is decreased by 15% to 85.
To make 85 back to 100 we divide it by the decrease (1-0.15):
85 / 0.85 = 100
To find out how much 85 increased to get back to 100, we do:
15 / 85 = 0.1765 = %17.65
15 is the reduction/difference, and 85 is the with reduction total.
Because percentages stay the same, this is applicable to any numbers, from this, we know that whenever something is reduced by 15% - when restored to it's original is increased by %17.65
The answer is %17.65
