-20.19% is the change from 639 to 510
Calculation steps:
[( 510 - 639 ) ÷ 639] x 100 = -20.19%
Formula
Percentage change = [(510 - 639) / 639] x 100
Subtract the new number by the original number
510 - 639 = -129
-129 ÷ 639 = -0.20187793427230047
-0.20187793427230047 x 100 = -20.19%