Total number of atoms for 5 mol => 5 x Na => 30 x 10^23 atoms.
And for HCP total no. of octahederal voids = Total no. of atoms present.
Hence No. of octahedral voids = 3 x 10^24
And No. of tetrahedral voidsd = 2 x no. of octahederal voids => 6 x 10^24.
Total no. of voids = > 9 x 10^23.