Suppose that in the short run, the firm which has production functionF(L, M) = 4L^1/2M^1/2must use 9 machines. If the cost of labor is $5 per unit and the cost of machines is $5 per unit, the short-run total cost of producing 108 units of output is

a. $900

b. $540

c. $500

d. $450

e. $600