$4-1($a$)$ Interstitials in the fcc lattice occupy the tetrahedral positions $(\frac{1}{4},\frac{1}{4},\frac{1}{4})$ and the octahedral

positions $(\frac{1}{2},\frac{1}{2},\frac{1}{2}).$ Indicate these interstitial positions on a sketch of the structure cell

$($b$)$ In the bcc lattice interstitials occupy sites at $(\frac{1}{2},\frac{1}{4},0)$ and smaller sites at $(\frac{1}{2},\frac{1}{2},0)$ and $(\frac{1}{2},0,0).$

Show these sites on a sketch.

Compare the number of available interstitial sites in the fcc and bcc lattices.