Mr Logan needs to buy snacks for his daughter soccer team. He decides to buy crackers and granola bars at a local store. The price of the crackers is $9 for 3 boxes, and the price of the granola bars is $6 for 3 boxes. Mr Logan ends up buying $20 worth of crackers and granola bars. Which equation represents the relationship between the number of boxes of crackers, x, and the number of boxes of granola bars, y, that Mr Logan bought at the grocery store.