In case of Schottky defects =$4\times \big(1-\large\frac{0.1}{100}\big)$$=3.996$
Thus density can be determined using
$\rho=\large\frac{Mz}{N_0a^3}$
$a=0.556nm=0.556\times 10^{-9}m$
$\Rightarrow 0.556\times 10^{-7}cm$
$\rho$(with Schottky defects)=$\large\frac{40\times 3.996}{6.023\times 10^{23}\times (0.556\times 10^{-7})^3}$
$\Rightarrow 1.5440g/cm^3$