How many total voids are present in $1 \ mol$ of a compound that forms an $hcp$ structure?

The volume occupied by the atoms in a unit cell of hexagonal close packing $(HCP)$ or cubic close packing $(CCP)$ is equal to:

$A$ compound is formed by two elements $M$ and $N$. The element $N$ forms $ccp$ lattice and atoms of $M$ occupy $1/3$ of the tetrahedral voids. What is the formula of the compound?

$A$ compound is formed by two elements $A$ and $B$. The atoms of element $B$ form $ccp$ structure. The atoms of $A$ occupy $1/3$ of tetrahedral voids. What is the formula of the compound?

$A$ binary solid has a zinc blende structure with $B$ ions constituting the lattice and $A$ ions occupying $25\%$ of the tetrahedral holes. The formula of the solid is:

In a crystal lattice,$C$ anions form a cubic close-packed $(CCP)$ structure. Cations $(A)$ occupy $50\%$ of the tetrahedral voids and cations $(B)$ occupy $50\%$ of the octahedral voids. Determine the molecular formula of the compound.