-21.28% is the change from 813 to 640
Calculation steps:
[( 640 - 813 ) ÷ 813] x 100 = -21.28%
Formula
Percentage change = [(640 - 813) / 813] x 100
Subtract the new number by the original number
640 - 813 = -173
-173 ÷ 813 = -0.21279212792127922
-0.21279212792127922 x 100 = -21.28%