In a factory, machine 1 produces 8-inch (in.) pliers at the rate of 60 units per hour and 6-inch pliers at the rate of 70 units per hour. Machine 2 produces 8-inch pliers at a rate of 40 units per hour and 6-inch pliers at the rate of 20 units per hour. It costs $50/hour to operate machine 1 and machine 2 costs $30/hour to operate. The production schedule requires at least 240 units of 8-inch pliers and at least 140 units of 6-inch pliers be produced during each 10-hour day. Which combination of machines will cost the least money to operate? Show you work completely.