For a BCC unit cell, (a) how many atoms are there inside the unit cell, (b) what is the coordination

For a BCC unit cell, (a) how many atoms are there inside the unit cell, (b) what is the coordination number for the atoms, (c) what is the relationship between the length of the side a of the BCC unit cell and the radius of its atoms, and (d) what is the atomic packing factor?