-84.35% is the change from 639 to 100
Calculation steps:
[( 100 - 639 ) ÷ 639] x 100 = -84.35%
Formula
Percentage change = [(100 - 639) / 639] x 100
Subtract the new number by the original number
100 - 639 = -539
-539 ÷ 639 = -0.8435054773082942
-0.8435054773082942 x 100 = -84.35%