Please Explain.

A competitive rm produces output using one xed factor and one variable factor. The rm's short run production function is X = 400L 2L2, where L is the amount of variable factor used. The price of output is $2 per unit and the price of the variable factor is $40 per unit. In the short run, how many units of L should the rm use? 31.66 80 200 95 None of the above. 999