The position vectors of three particles of mass $m_{1}=1 \mathrm{~kg}, m_{2}=2 \mathrm{~kg}$ and $m_{3}=3 \mathrm{~kg}$ are $\vec{r}_{1}-(\hat{i}|4 \hat{j}| \hat{k}) m, \vec{r}_{2}-(\hat{i}|\hat{j}| \hat{k}) m$ and $\vec{r}_{3}-(2 \hat{i} \quad \hat{j} \quad 2 \hat{k})$ respectively. Find the position vec-
tor of their centre of mass.