-19.39% is the change from 820 to 661
Calculation steps:
[( 661 - 820 ) ÷ 820] x 100 = -19.39%
Formula
Percentage change = [(661 - 820) / 820] x 100
Subtract the new number by the original number
661 - 820 = -159
-159 ÷ 820 = -0.19390243902439025
-0.19390243902439025 x 100 = -19.39%