-20.12% is the change from 840 to 671
Calculation steps:
[( 671 - 840 ) ÷ 840] x 100 = -20.12%
Formula
Percentage change = [(671 - 840) / 840] x 100
Subtract the new number by the original number
671 - 840 = -169
-169 ÷ 840 = -0.2011904761904762
-0.2011904761904762 x 100 = -20.12%