Peter owns an auto parts firm. He uses a combination of steel and aluminum to produce her auto parts. All of the following combinations will finish the task on time. Steel costs $15 per unit and the aluminum costs $50 per unit. What combination of steel and aluminum should he use?
- 15 units of steel and 7 units of aluminum
- 10 units of steel and 10 units of aluminum
- 20 units of steel and 6 units of aluminum
- 7 units of steel and 15 units of aluminum