100% is the change from 15 to 30
Calculation steps:
[( 30 - 15 ) ÷ 15] x 100 = 100%
Formula
Percentage change = [(30 - 15) / 15] x 100
Subtract the new number by the original number
30 - 15 = 15
15 ÷ 15 = 1
1 x 100 = 100%
Example