A production function has the property that f( xL, xK) = x2f( L, K) for any positive

Question:

A production function has the property that f( xL, xK) = x2f( L, K) for any positive value of x. What kind of returns to scale does this production function exhibit? If the firm doubles L and K, show that the marginal product of labor and the marginal product of capital also double.