A farmer uses two types of fertilizers. A 50-lb bag of Fertilizer A contains 8 lb of nitrogen, 2 lb of phosphorus, and 4 lb of potassium. A 50 lb bag of Fertilizer B contains 5 lb. each of nitrogen, phosphorus, and potassium. The minimum requirements for a field are 440 lb of nitrogen, 260 lb of phosphorus, and 360 lb of potassium. If a 50-lb bag of Fertilizer A costs $70 and a 50-lb bag of Fertilizer B costs $60, find the amount of each type of fertilizer the farmer should use to minimize his cost while still meeting the minimum requirement