The graph below shows the price, y, in dollars, of different amounts of peanuts, x, in pounds:

A graph titled Peanut Prices shows Number of Pounds on x axis and Price in dollars on y axis. The scale on the x axis shows numbers from 0 to 12 at increments of 2, and the scale on the y axis shows numbers from 0 to 36 at increments of 6. A straight line joins the ordered pairs 0, 0 and 12, 36.

Which equation best represents the relationship between x and y?