-23.1% is the change from 840 to 646
Calculation steps:
[( 646 - 840 ) ÷ 840] x 100 = -23.1%
Formula
Percentage change = [(646 - 840) / 840] x 100
Subtract the new number by the original number
646 - 840 = -194
-194 ÷ 840 = -0.23095238095238096
-0.23095238095238096 x 100 = -23.1%