Concern the cost, C, of renting a car from a company which charges $40 a day and 15 cents a mile, so C = f(d, m) = 40d + 0.15m, where d is the number of days, and m is the number of miles.

(a) Find f(3, 200) and interpret it.
(b) Explain the significance of f(3,m) in terms of rental car costs. Graph this function, with C as a function of m.
(c) Explain the significance of f(d, 100) in terms of rental car costs. Graph this function, with C as a function of d.