-66.41% is the change from 640 to 215
Calculation steps:
[( 215 - 640 ) ÷ 640] x 100 = -66.41%
Formula
Percentage change = [(215 - 640) / 640] x 100
Subtract the new number by the original number
215 - 640 = -425
-425 ÷ 640 = -0.6640625
-0.6640625 x 100 = -66.41%