-21.98% is the change from 819 to 639
Calculation steps:
[( 639 - 819 ) ÷ 819] x 100 = -21.98%
Formula
Percentage change = [(639 - 819) / 819] x 100
Subtract the new number by the original number
639 - 819 = -180
-180 ÷ 819 = -0.21978021978021978
-0.21978021978021978 x 100 = -21.98%