A machine part to be machined may be made either from an alloy of aluminum or steel. There is an order for 7,000 units. Steel costs 8.00 per kg, while aluminum costs 13.00 per kg. If steel is used, the steel per unit weighs 100 grams; for aluminum, 25 grams. When steel is used, 60 units can be produced per hour; for aluminum, 100 units per hour with the aid of a tool costing 800.00, which will be useless after the 8,000 units are finished. The cost of the machine and operator is 100.00 per hour. If all other costs are identical, determine which material will be more economical.