5.  Suppose that a firm's cost per unit of labor is $100 per day and its cost per unit of capital is $400 per day.

a.  Draw the isocost line for a total cost per day of $2000.

b.  If the firm is producing efficiently, what is the marginal rate of technical substitution between labor and capital?

c.  Demonstrate your answer to part (b) using isocost lines and isoquant curves.