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.

Make a table of values for C, using d = 1, 2, 3, 4 and m = 100, 200, 300, 400. You should have 16 values in your table.