A) P(x) = 1.078x (considering that the 7.8% tax (0.078) is added to the price, x.
b) D(x) = x + 65 (the delivery fee is $65)
c) P(D(x)) = P(x+65) = 1.078(x + 65) = 1.078x + 70.07
D(P(x)) = D(1.078x) = 1.078x + 65
D(P(x)) is cheaper, as 65 < 70.07
If there's the law, P(D(x)) will be complaint. Because in it, the tax is being added to the delivery fee.