The King Concrete Company manufactures bags of concrete mix from beach sand and river sand. Each pound of beach sand costs 5 cents and contains 4 units of ne sand, 3 units of coarse sand and 5 units of gravel. Each pound of river sand costs 10 cents and contains 3 units of ne sand, 6 units of coarse sand, and 12 units of gravel. Each bag of concrete must contain at least 12 units of ne sand, 12 units of coarse sand and 10 units of gravel. Find the best combination of beach sand and river sand which will meet the minimum requirements of ne sand, coarse sand, and gravel at the least cost, and indicate the cost per pound