Step 1: Create a linear function that uses the number of miles driven as the input and provides the total car rental cost (including gas) for Dustin's entire trip as the output.

To find the slope of the linear function compute the cost per mile by adding the mileage fee and the cost of gas per mile. Hint: to find the cost of gas per mile divide the cost per gallon by the miles per gallon. The "gallons" units cancel leaving the units "dollars per mile"