-19.53% is the change from 640 to 515
Calculation steps:
[( 515 - 640 ) ÷ 640] x 100 = -19.53%
Formula
Percentage change = [(515 - 640) / 640] x 100
Subtract the new number by the original number
515 - 640 = -125
-125 ÷ 640 = -0.1953125
-0.1953125 x 100 = -19.53%