#### Answer

If $y$ equals the total cost and $x$ equals the total miles:
(a) Proxy car rental: $y=.32x+18$
(b) YourPal car rental: $y=.36x+12$
(c) Proxy

#### Work Step by Step

To find the function of a rental company, we multiply the cost per mile by $x$ and add the surcharge.
We multiply the cost per mile by the total miles to get the amount paid from the miles. $\frac{cost}{mile}\times mile=cost$. We then add the surcharge to finish the function.
(c) We substitute 820 into the functions
Proxy: $.32(820)+18=280.4$
YourPal: $.36(820)+12=307.2$
Proxy offers a better deal.