-98.9% is the change from 815 to 9
Calculation steps:
[( 9 - 815 ) ÷ 815] x 100 = -98.9%
Formula
Percentage change = [(9 - 815) / 815] x 100
Subtract the new number by the original number
9 - 815 = -806
-806 ÷ 815 = -0.9889570552147239
-0.9889570552147239 x 100 = -98.9%