-37.81% is the change from 640 to 398
Calculation steps:
[( 398 - 640 ) ÷ 640] x 100 = -37.81%
Formula
Percentage change = [(398 - 640) / 640] x 100
Subtract the new number by the original number
398 - 640 = -242
-242 ÷ 640 = -0.378125
-0.378125 x 100 = -37.81%