Molecular mass of $\left[\left( NH _{2}\right)_{2} CO \right]=60 g / mol$

$\therefore$ No. of moles $=\frac{0.0100}{60.06}=1.67 \times 10^{-4} mol$

Now, Mass $=$ Volume $\times$ Density

Density of water $=10^{3} g / dm ^{3}$ and Volume $=0.3000 dm ^{3}$

$\therefore$ Mass of water $=0.3000 \times 10^{3}=300 g =0.3 kg$

Molality $=\frac{\text { Moles of solute }}{\text { Mass of solvent(kg) }}=\frac{1.67 \times 10^{-4}}{0.3}=5.57 \times 10^{-4} m$