-80% is the change from 90 to 18
Calculation steps:
[( 18 - 90 ) ÷ 90] x 100 = -80%
Formula
Percentage change = [(18 - 90) / 90] x 100
Subtract the new number by the original number
18 - 90 = -72
-72 ÷ 90 = -0.8
-0.8 x 100 = -80%
Example