-89.67% is the change from 639 to 66
Calculation steps:
[( 66 - 639 ) ÷ 639] x 100 = -89.67%
Formula
Percentage change = [(66 - 639) / 639] x 100
Subtract the new number by the original number
66 - 639 = -573
-573 ÷ 639 = -0.8967136150234741
-0.8967136150234741 x 100 = -89.67%