I'm unsure what to insert for the Fermi energy, Ef!

An estimate of the total number of occupied states can be obtained by integrating the density of states from 0 to the Fermi level. N=0EFN(E)dE=(2meEF)3/2V/323 Calculate the total number of occupied states for a sodium crystal of volume (a) 1012m3, (b) 106 m3, and (c) 1029m3 (approximately atomic size). Compare your results with the number of electrons available and comment on the different answers to (a), (b) and (c). A crystal of volume 1012m3 contains 2.51016 atoms