-20% is the change from 15 to 12
Calculation steps:
[( 12 - 15 ) ÷ 15] x 100 = -20%
Formula
Percentage change = [(12 - 15) / 15] x 100
Subtract the new number by the original number
12 - 15 = -3
-3 ÷ 15 = -0.2
-0.2 x 100 = -20%
Example