-90% is the change from 180 to 18
Calculation steps:
[( 18 - 180 ) ÷ 180] x 100 = -90%
Formula
Percentage change = [(18 - 180) / 180] x 100
Subtract the new number by the original number
18 - 180 = -162
-162 ÷ 180 = -0.9
-0.9 x 100 = -90%
Example