-90.36% is the change from 840 to 81
Calculation steps:
[( 81 - 840 ) ÷ 840] x 100 = -90.36%
Formula
Percentage change = [(81 - 840) / 840] x 100
Subtract the new number by the original number
81 - 840 = -759
-759 ÷ 840 = -0.9035714285714286
-0.9035714285714286 x 100 = -90.36%