What is the coordination number of a cation in an ionic compound if the type of hole occupied by the cation is octahedral?

The coordination number for $Cu$ (Copper) in its crystal structure is:

$A$ cubic structure is formed where atoms of element $X$ are occupied at the corners of the cube and also at the face centers. Atoms of element $Y$ are present at the body center and at the edge centers. If all the atoms are removed along a plane passing through the middle of the cube (bisecting the four edges), the formula will become

If $Z$ is the number of atoms in the unit cell that represents the closest packing sequence $ABCABC$,the number of tetrahedral voids in the unit cell is equal to

Number of atoms per unit cell for body centered cubic system is

In a face-centred cubic $(FCC)$ lattice,atoms of $A$ form the corner points and atoms of $B$ form the face-centred points. If two atoms of $A$ are missing from the corner points,the formula of the ionic compound is