-6.32% is the change from 870 to 815
Calculation steps:
[( 815 - 870 ) ÷ 870] x 100 = -6.32%
Formula
Percentage change = [(815 - 870) / 870] x 100
Subtract the new number by the original number
815 - 870 = -55
-55 ÷ 870 = -0.06321839080459771
-0.06321839080459771 x 100 = -6.32%