-17.5% is the change from 640 to 528
Calculation steps:
[( 528 - 640 ) ÷ 640] x 100 = -17.5%
Formula
Percentage change = [(528 - 640) / 640] x 100
Subtract the new number by the original number
528 - 640 = -112
-112 ÷ 640 = -0.175
-0.175 x 100 = -17.5%