-15.94% is the change from 640 to 538
Calculation steps:
[( 538 - 640 ) ÷ 640] x 100 = -15.94%
Formula
Percentage change = [(538 - 640) / 640] x 100
Subtract the new number by the original number
538 - 640 = -102
-102 ÷ 640 = -0.159375
-0.159375 x 100 = -15.94%