How much part of an atom occupies each corner of a $bcc$ unit cell?

$A$ solid compound is formed by atoms of $A$ (cations),$B$ (cations),and $O$ (anions). Atoms of $O$ form an $hcp$ lattice. Atoms of $A$ occupy $25\%$ of the tetrahedral voids,and atoms of $B$ occupy $50\%$ of the octahedral voids. What is the molecular formula of the solid?

What fraction of one edge-centred octahedral void lies in one unit cell of $fcc$?

What type of crystal structure from the following has $52.36 \%$ packing efficiency?

Atoms $A$ are arranged in an $FCC$ system,and atoms $B$ occupy all the octahedral voids and half of the tetrahedral voids. The formula of the compound is:

$A$ two-dimensional solid is made by alternating circles with radius $a$ and $b$ such that the sides of the circles touch. The packing fraction is defined as the ratio of the area under the circles to the area under the rectangle with sides of length $x$ and $y$. The ratio $r=b/a$ for which the packing fraction is minimised is closest to $.....$