An independent trucker has the following options. If he buys expensive machinery, then he can hire fewer drivers to deliver the same output. Over the course of this month, he has to deliver to 50 spots. To do this job, he has 4 possible combinations of output that he can use:
Method 1: 100 drivers, 0 machines
Method 2: 10 drivers, 12 machines
Method 3: 20 drivers, 10 machines
Method 4: 50 drivers, 2 machines
Hiring a driver costs $10. Each machine costs $100. Which method should he use?