d = days rented for
m = miles driven for
so the cost of the car is 35 bucks a day and 45 cents or $0.45 per mile driven, let's check it out for say a few days
1st day, 3 miles......................35(1) + 0.45(3)
2nd day, 2 miles..................35(2) + 0.45(2)
3rd day, say 5 miles............35(3) + 0.45(5)
dth day, and m miles..........35d + 0.45m
so the cost function could be written as C = 35d+0.45m.
now, we know for 2 days, d = 2, it cost 166.75 bucks, so