28.80 + .20X = X
.20X = X - 28.80
1/5 = .20
X/5 = X -28.80
X = 5X - 144
Set the new X equal to the original X
28.80 + .20X = 5X - 144
172.8 + .20X = 5X
172.8 = 4.8X
36 = X
36$ is the original price
To check,
28.80 + (.20 x 36) = 36
28.80 + 7.2 = 36
36 = 36