A firm purchases capital and labour in compeitive markets at prices of r= $6/machine-hour and w=$4/ labour-hours, respectively. With the firm's current input mix, the marginal prodcut of capital is 12 kg/ machine-hour and the marginal product of labour is 18kg/ labour-hour. Is this firm minimizing its costs? If so, explain how you know, If not, explain what the firm ought to do.