An animal feed to be mixed from soybean meal and oats must contain at least 120lb of protein, 21lb of fat, and 10lb of mineral ash. Each sack of soybeans costs $15 and contains 50lb of protein, 77lb of fat, and 5lb of mineral ash. Each sack of oats costs $5and contains 15lb of protein, 5lb of fat, and 1 lb of mineral ash. How many sacks of each should be used to satisfy the minimum requirements at minimum cost?