[Kilgore Trout]

Hello, this is my first introduction to undergraduate inorganic chemistry. So far so good until recently when we started covering ionic solids. I need some guidance on how to solve this problem. It reads:

Identify the stoichiometries of the following structures based on hole filling using a cation "A", in close-packed arrays of anions "X".

(a) An hcp array in which one-third of the octahedral sites are filled.
(b) A ccp array in which all the tetrahedral and all the octahedral sites are filled.

I know that for an array of "n" atoms in a closed packed structure gives rise to "n" octahedral holes. And also, "n" atoms gives rise to "2n" tetrahedral holes. How should I apply these principles into solving determining the stoichiometry? HCP is no doubt close packed, as is ccp (which is also fcc and it cotains 4 atoms inside one unit cell).