-96.72% is the change from 640 to 21
Calculation steps:
[( 21 - 640 ) ÷ 640] x 100 = -96.72%
Formula
Percentage change = [(21 - 640) / 640] x 100
Subtract the new number by the original number
21 - 640 = -619
-619 ÷ 640 = -0.9671875
-0.9671875 x 100 = -96.72%