-69.8% is the change from 255 to 77
Calculation steps:
[( 77 - 255 ) ÷ 255] x 100 = -69.8%
Formula
Percentage change = [(77 - 255) / 255] x 100
Subtract the new number by the original number
77 - 255 = -178
-178 ÷ 255 = -0.6980392156862745
-0.6980392156862745 x 100 = -69.8%