A competitive firm uses two inputs, capital () and labour (), to produce one output, (). The price of capital, _k, is $1 per unit and the price of labor, _l, is $1 per unit. The firm operates in competitive markets for outputs and inputs, so takes the prices as given. The production function is (,)=3^{0.25 0.25}.

Using your supply function, find the profit maximising quantity if the price of output =4. What price would be needed for the firm to supply 18 units of output?