Y= 9x. If 27 dollars is the cost for 3 hours, finding the price for one hour is simple. You would take the cost divided by the time. The slope would be 9 because if you graphed (1,9) (2,18) and (3,27) [the costs per the hours] you could find that, what I use, rise over run. Basically, you can count how far from two points to get slope. Starting with the y, from 9 to 18 is 9. Then, with x, 2 to 1 is 1. So, the slope is 9/1 or 9