-90% is the change from 850 to 85
Calculation steps:
[( 85 - 850 ) ÷ 850] x 100 = -90%
Formula
Percentage change = [(85 - 850) / 850] x 100
Subtract the new number by the original number
85 - 850 = -765
-765 ÷ 850 = -0.9
-0.9 x 100 = -90%
Example