Final answer:
The company should use Method 3 as it has the lowest total cost.
Step-by-step explanation:
To determine the best production method, we need to calculate the total cost for each method. Method 1 would have a total cost of $7,000 (50 units of labor x $100/unit + 10 units of capital x $400/unit). Method 2 would have a total cost of $8,000 (20 units of labor x $100/unit + 40 units of capital x $400/unit), and Method 3 would have a total cost of $7,000 (10 units of labor x $100/unit + 70 units of capital x $400/unit). Therefore, the company should use Method 3 as it has the lowest total cost.