4. (5 pts) A company nds that when a product is priced at p dollars per unit, q units of the product will be sold where q = 13 - 7p. The company's cost for producing q units of the product is given by C(q) = g + 1600. (a) Determine a function P(q) that gives the company's prot earned on the sale of q units. (b) 011 which interval is the function P(q) an increasing function of