-19.86% is the change from 831 to 666
Calculation steps:
[( 666 - 831 ) ÷ 831] x 100 = -19.86%
Formula
Percentage change = [(666 - 831) / 831] x 100
Subtract the new number by the original number
666 - 831 = -165
-165 ÷ 831 = -0.19855595667870035
-0.19855595667870035 x 100 = -19.86%