-18.94% is the change from 639 to 518
Calculation steps:
[( 518 - 639 ) ÷ 639] x 100 = -18.94%
Formula
Percentage change = [(518 - 639) / 639] x 100
Subtract the new number by the original number
518 - 639 = -121
-121 ÷ 639 = -0.18935837245696402
-0.18935837245696402 x 100 = -18.94%