-21.13% is the change from 639 to 504
Calculation steps:
[( 504 - 639 ) ÷ 639] x 100 = -21.13%
Formula
Percentage change = [(504 - 639) / 639] x 100
Subtract the new number by the original number
504 - 639 = -135
-135 ÷ 639 = -0.2112676056338028
-0.2112676056338028 x 100 = -21.13%