-86.7% is the change from 639 to 85
Calculation steps:
[( 85 - 639 ) ÷ 639] x 100 = -86.7%
Formula
Percentage change = [(85 - 639) / 639] x 100
Subtract the new number by the original number
85 - 639 = -554
-554 ÷ 639 = -0.86697965571205
-0.86697965571205 x 100 = -86.7%