-2.97% is the change from 640 to 621
Calculation steps:
[( 621 - 640 ) ÷ 640] x 100 = -2.97%
Formula
Percentage change = [(621 - 640) / 640] x 100
Subtract the new number by the original number
621 - 640 = -19
-19 ÷ 640 = -0.0296875
-0.0296875 x 100 = -2.97%