What kind of formula do i use to find out the cheapest rate to use for the car rental?

Question

Mr. Smith wants to rent a Suv to go from home to a conference in Seattle, he expects to do 350 miles in total during this journey
There are 3 rental companies:
Hertzy Rental-Fixed rate of $58 dollars with no mileage charge
Alabo Rental-Charge $.35 cents per mile
Nifty Rental-Charge a fixed rate of $28 plus $.15 cents per mile

Answer 1

charge for x miles:
Hertz: 58
Alabo: .35x
Nifty: 28 + .15x

so, for 350 miles, you get

Hertz: 58.00
Alabo: .35(350) = 122.50
Nifty: 28 + .15(350) = 80.50

I guess it's easy now to tell which is cheapest for a 350-mile rental.