-90.36% is the change from 830 to 80
Calculation steps:
[( 80 - 830 ) ÷ 830] x 100 = -90.36%
Formula
Percentage change = [(80 - 830) / 830] x 100
Subtract the new number by the original number
80 - 830 = -750
-750 ÷ 830 = -0.9036144578313253
-0.9036144578313253 x 100 = -90.36%