Here is how I would work out the problem.
First, convert density to g/pm^3
(16.654g/cm^3)x(1cm^3/10^30pm^3) = 1.6654x10^-32 g/pm^3
Then, calculate weight of a unit cell by multiplying density by volume
(1.6654x10^-32 g/pm^3) x (330.29pm)^3 = 6 x 10^-22 g / unit cell
Since there are two atoms in the unit cell, weight of one atom is 3 x 10^-22 g
Finally, 180.949g / Avogadro's No. = weight of an atom = 3 x 10^-22g
Solve the equation and there you go.