Suppose that a firm's production function is given by Q = 3L + 6K, where L and K stand for hours of labor and capital used respectively. The firm wants to produce 60 units of output, and the current wage rate (w) is $2, while the rental rate (r) is $6. If the firm chooses its input combination optimally, how much will it cost the firm to produce this output?
a) 53.36
b) 40
c) 120
d) 60