-39.4% is the change from 840 to 509
Calculation steps:
[( 509 - 840 ) ÷ 840] x 100 = -39.4%
Formula
Percentage change = [(509 - 840) / 840] x 100
Subtract the new number by the original number
509 - 840 = -331
-331 ÷ 840 = -0.39404761904761904
-0.39404761904761904 x 100 = -39.4%