-90.59% is the change from 850 to 80
Calculation steps:
[( 80 - 850 ) ÷ 850] x 100 = -90.59%
Formula
Percentage change = [(80 - 850) / 850] x 100
Subtract the new number by the original number
80 - 850 = -770
-770 ÷ 850 = -0.9058823529411765
-0.9058823529411765 x 100 = -90.59%