3) Determine the stoichiometry (e.g., AnXm) of the following ionic solid unit cell structures derived from hole filling in close-packed arrays of anions (X) with: (a) half the octahedral holes filled with cations (A); (b) one-quarter of the tetrahedral holes filled with cations (A); and (c) two-thirds of the octahedral holes filled with cations (A). What are the expected coordination numbers for the structures in (a) and (b)