Calculate the density of states per unit volume of a three-dimensional nearly free electron gas with effective mass m* in a magnetic field B_z perpendicular to the x-y plane including spin. Remember that the number of allowed ky states per Landau level is given b_y L_x L_y q_B /h for an area of size LxL_z and that there is another (free electron) z-degree of freedom in the z-direction.