-85.76% is the change from 639 to 91
Calculation steps:
[( 91 - 639 ) ÷ 639] x 100 = -85.76%
Formula
Percentage change = [(91 - 639) / 639] x 100
Subtract the new number by the original number
91 - 639 = -548
-548 ÷ 639 = -0.8575899843505478
-0.8575899843505478 x 100 = -85.76%