-18.18% is the change from 99 to 81
Calculation steps:
[( 81 - 99 ) ÷ 99] x 100 = -18.18%
Formula
Percentage change = [(81 - 99) / 99] x 100
Subtract the new number by the original number
81 - 99 = -18
-18 ÷ 99 = -0.18181818181818182
-0.18181818181818182 x 100 = -18.18%