Car rent : $80
Cost per mile : $20
Additional insurance : $40
mile = x
To calculate the total cost (y) of renting a car for a customer who decides to buy the optional insurence, we have to add the fixed cost of the Car rental (80) and the cost of the insurance (40), plus the product ot the cost per mile (20) and the number of miles.
y= 80+40+20x
y= 120+20x