-84.51% is the change from 639 to 99
Calculation steps:
[( 99 - 639 ) ÷ 639] x 100 = -84.51%
Formula
Percentage change = [(99 - 639) / 639] x 100
Subtract the new number by the original number
99 - 639 = -540
-540 ÷ 639 = -0.8450704225352113
-0.8450704225352113 x 100 = -84.51%