-33.13% is the change from 640 to 428
Calculation steps:
[( 428 - 640 ) ÷ 640] x 100 = -33.13%
Formula
Percentage change = [(428 - 640) / 640] x 100
Subtract the new number by the original number
428 - 640 = -212
-212 ÷ 640 = -0.33125
-0.33125 x 100 = -33.13%