-20.64% is the change from 809 to 642
Calculation steps:
[( 642 - 809 ) ÷ 809] x 100 = -20.64%
Formula
Percentage change = [(642 - 809) / 809] x 100
Subtract the new number by the original number
642 - 809 = -167
-167 ÷ 809 = -0.20642768850432633
-0.20642768850432633 x 100 = -20.64%