A firm is using 500 units of capital and 200 units of labor to produce 10,000 units of output.

Capital costs $100 per unit and labor $20 per unit.The last unit of capital added 50 units of output, while the last unit of labor added 20 units of output.The firm

1) is using the cost-minimizing combination of capital and labor.

2 )should use more of both inputs in equal proportions.

3) should use less of both inputs in equal proportions.

4)could produce the same level of output at a lower cost by using more capital and less labor.

5) could produce the same level of output at a lower cost by using less capital and more labor.