-2.74% is the change from 657 to 639
Calculation steps:
[( 639 - 657 ) ÷ 657] x 100 = -2.74%
Formula
Percentage change = [(639 - 657) / 657] x 100
Subtract the new number by the original number
639 - 657 = -18
-18 ÷ 657 = -0.0273972602739726
-0.0273972602739726 x 100 = -2.74%