-20.31% is the change from 320 to 255
Calculation steps:
[( 255 - 320 ) ÷ 320] x 100 = -20.31%
Formula
Percentage change = [(255 - 320) / 320] x 100
Subtract the new number by the original number
255 - 320 = -65
-65 ÷ 320 = -0.203125
-0.203125 x 100 = -20.31%