-85.92% is the change from 639 to 90
Calculation steps:
[( 90 - 639 ) ÷ 639] x 100 = -85.92%
Formula
Percentage change = [(90 - 639) / 639] x 100
Subtract the new number by the original number
90 - 639 = -549
-549 ÷ 639 = -0.8591549295774648
-0.8591549295774648 x 100 = -85.92%