Tell whether x and y are proportional

Look at the following graph of the given equation. determine whether the equation is a function. explain why or why not.

Part a: sam rented a boat at $225 for 2 days. if he rents the same boat for 5 days, he has to pay a total rent of $480. write an equation in the standard form to represent the total rent (y) that sam has to pay for renting the boat for x days. (4 points)

Me. i can't figure out this question. give an explanation too. .