-22.5% is the change from 400 to 310
Calculation steps:
[( 310 - 400 ) ÷ 400] x 100 = -22.5%
Formula
Percentage change = [(310 - 400) / 400] x 100
Subtract the new number by the original number
310 - 400 = -90
-90 ÷ 400 = -0.225
-0.225 x 100 = -22.5%