-10.93% is the change from 915 to 815
Calculation steps:
[( 815 - 915 ) ÷ 915] x 100 = -10.93%
Formula
Percentage change = [(815 - 915) / 915] x 100
Subtract the new number by the original number
815 - 915 = -100
-100 ÷ 915 = -0.1092896174863388
-0.1092896174863388 x 100 = -10.93%