-8.08% is the change from 99 to 91
Calculation steps:
[( 91 - 99 ) ÷ 99] x 100 = -8.08%
Formula
Percentage change = [(91 - 99) / 99] x 100
Subtract the new number by the original number
91 - 99 = -8
-8 ÷ 99 = -0.08080808080808081
-0.08080808080808081 x 100 = -8.08%