This is my third attempt and each way I do the equation it states I'm wrong so if you would help that would be great. I believe it's because I can't put into the form of (CW)

municipal water supply are billed a fixed amount monthly plus a charge for each cubic foot of water used. A household using 2000 cubic feet was billed $155, while one using 2800 cubic feet was billed $195. (a) What is the charge per cubic foot? 0.05 dollars per cubic foot (b) Write an equation for the total cost, c, of a resident's water, w, as a function of cubic feet of water used. c(w) dollars (c) How many cubic feet of water used would lead to a bill of $210? cubic feet