-19.09% is the change from 791 to 640
Calculation steps:
[( 640 - 791 ) ÷ 791] x 100 = -19.09%
Formula
Percentage change = [(640 - 791) / 791] x 100
Subtract the new number by the original number
640 - 791 = -151
-151 ÷ 791 = -0.19089759797724398
-0.19089759797724398 x 100 = -19.09%