Shakespear's Pizza sells 1 comma 100 large Vegi Pizzas per week for ​$18 a pizza. When the owner offers a​ $5 discount, the weekly sales increase to 1 comma 600. ​(a) Assume a linear relation between the weekly sales​ A(x) and the discount x. Find​ A(x). ​(b) Find the value of x that maximizes the weekly revenue. ​(c) Answer parts​ (a) and​ (b) if the price of one pizza is ​$9 and all other data are unchanged.