6. (20 points) Assume a firm is producing 1,000 units of output and their total cost is $12,000 Further assume that at the current levels of K and L being used, hiring one more unit of L would increase output by 20 units of output while hiring two more units of capital would also increase output by 20 units. Explain how you know they are currently producing at input mix a, b, or c. K 120 a b c 150