Suppose that sales are related to advertising expenditures according to one of the following two models, where S1 and Sn are sales and x is advertising, all in millions of dollars.

S1 = 30 + 20x - 0.4x2

Sn = 24.58 + 325.18(1 - e-x/14)

(a) Graph both of these functions on the same set of axes. Use a graphing utility.

(b) Do these two functions give approximately the same sales per million dollars of advertising for 0 ≤ x ≤ 20?

(c) How do these functions differ for x20? Which more realistically represents the relationship between sales and advertising expenditures after $20 million is spent on advertising? Why?