-3.15% is the change from 635 to 615
Calculation steps:
[( 615 - 635 ) ÷ 635] x 100 = -3.15%
Formula
Percentage change = [(615 - 635) / 635] x 100
Subtract the new number by the original number
615 - 635 = -20
-20 ÷ 635 = -0.031496062992125984
-0.031496062992125984 x 100 = -3.15%