-25.9% is the change from 830 to 615
Calculation steps:
[( 615 - 830 ) ÷ 830] x 100 = -25.9%
Formula
Percentage change = [(615 - 830) / 830] x 100
Subtract the new number by the original number
615 - 830 = -215
-215 ÷ 830 = -0.25903614457831325
-0.25903614457831325 x 100 = -25.9%