Set up an inequality for...?

A cat food manufacturer uses fish and beef byproducts. The fish contains 12 g of protein and 3 g of fat per ounce. The beef contains 6 g of protein and 9 g of fat per ounce. Each can of cat food must contain at lease 57 g of protein and 39 g of fat. Find a system of inequalities that describes the possible number of ounces of fish and beef that can be used in each can to satisfy these minimum requirements. (x is the number of ounces of fish and y is the number of ounces of beef.)