Suppose a firm’s production function is q = 5LK , where q is the level of output, L is the quantity of labour and K is the quantity of capital. For this production function, the marginal product of labour and capital are given by, respectively, MPL = 5K and MPK = 5L . The cost of one unit of labour is $20 and the rental cost of one unit capital is $80. If the firm were free to adjust the level of capital, find the cost-minimizing input bundle to produce 720 units of output.