When looking at the total cost of x pounds of something when the cost is per pound, you multiply the two numbers. Because y is the total cost, you want that as the answer that you are looking for, so it will be by itself when looking at the two sides of the equation. This means that answer c is the only one correct. A/B cannot be unless you were looking for the number of pounds, and you were dividing y (total cost) by 2.19 (cost per pound). D does not work because you are just adding how many pounds you have to the cost per pound.
