-99.06% is the change from 640 to 6
Calculation steps:
[( 6 - 640 ) ÷ 640] x 100 = -99.06%
Formula
Percentage change = [(6 - 640) / 640] x 100
Subtract the new number by the original number
6 - 640 = -634
-634 ÷ 640 = -0.990625
-0.990625 x 100 = -99.06%