What type of solid is the silica?

In a solid, $\mathrm{B}^{-}$ions occupy corners of a cube forming ccp structure. If $\mathrm{A}^{+}$ion occupy half the tetrahedral voids, formula of the solid is

Unit cell of an element has edge length of 5$$\mathop A\limits^o $$ with density $4 \mathrm{~g} \mathrm{~cm}^{-3}$, if its atomic mass is 149, identify the crystal structure.

What is the volume of one particle in BCC structure if ' $a$ ' is edge length?