-81.09% is the change from 640 to 121
Calculation steps:
[( 121 - 640 ) ÷ 640] x 100 = -81.09%
Formula
Percentage change = [(121 - 640) / 640] x 100
Subtract the new number by the original number
121 - 640 = -519
-519 ÷ 640 = -0.8109375
-0.8109375 x 100 = -81.09%