-21.69% is the change from 816 to 639
Calculation steps:
[( 639 - 816 ) ÷ 816] x 100 = -21.69%
Formula
Percentage change = [(639 - 816) / 816] x 100
Subtract the new number by the original number
639 - 816 = -177
-177 ÷ 816 = -0.21691176470588236
-0.21691176470588236 x 100 = -21.69%