-21.61% is the change from 819 to 642
Calculation steps:
[( 642 - 819 ) ÷ 819] x 100 = -21.61%
Formula
Percentage change = [(642 - 819) / 819] x 100
Subtract the new number by the original number
642 - 819 = -177
-177 ÷ 819 = -0.21611721611721613
-0.21611721611721613 x 100 = -21.61%