-3.75% is the change from 800 to 770
Calculation steps:
[( 770 - 800 ) ÷ 800] x 100 = -3.75%
Formula
Percentage change = [(770 - 800) / 800] x 100
Subtract the new number by the original number
770 - 800 = -30
-30 ÷ 800 = -0.0375
-0.0375 x 100 = -3.75%