-19.9% is the change from 799 to 640
Calculation steps:
[( 640 - 799 ) ÷ 799] x 100 = -19.9%
Formula
Percentage change = [(640 - 799) / 799] x 100
Subtract the new number by the original number
640 - 799 = -159
-159 ÷ 799 = -0.19899874843554444
-0.19899874843554444 x 100 = -19.9%