The position vector of 1 kg object is $\vec{r} = (3\hat{\mathrm{i}} - \hat{\mathrm{j}})\mathrm{~m}$ and its velocity $\vec{v} = (3\hat{\mathrm{j}} + \hat{\mathrm{k}})\mathrm{~m\,s^{-1}}$. The magnitude of its angular momentum is $\sqrt{x}\mathrm{~N\,m\,s}$, where $x$ is $\_\_\_\_$.