Economics Homework Help

I’m working on a Economics question and need guidance to help me study.

Suppose the hourly wage rate is $13, the rental price of capital is $3 and the price of output is constant at $30 per unit. Firm’s production technology is q = 4K^0.25E^0.75, the marginal product of employment is MP_E =3K^0.25E^-0.25 and the marginal product of capital is MP_K = K^-0.75E^0.75. What is firm’s optimal demand of labor if firm plans to produce q=20 units of outputs in the long-run? (please keep 1 decimal place in your answer).