-19.5% is the change from 800 to 644
Calculation steps:
[( 644 - 800 ) ÷ 800] x 100 = -19.5%
Formula
Percentage change = [(644 - 800) / 800] x 100
Subtract the new number by the original number
644 - 800 = -156
-156 ÷ 800 = -0.195
-0.195 x 100 = -19.5%