A researcher wants to provide a rabbit exactly 172 units of protein, 212 units of carbohydrates, and 40 units of vitamin A. The rabbit is fed three types of food. Each gram of Food A has 4 units of protein, 5 units of carbohydrates, and 1 unit of vitamin A. Each gram of Food B contains 9 units of protein, 11 units of carbohydrates, and 2 units of vitamin A. Each gram of Food C contains 15 units of protein, 18 units of carbohydrates, and 3 units of vitamin A. How many grams of each food should the rabbit be fed? There are an infinite number of solutions to this problem. Fill in expressions for the amount of foods A and B that the rabbit should be fed. Food A, x = Food B, y = Food C, z = any amount, within limitations (Simplify your answer. Type an expression for x and y in terms of z.)