Let $\overrightarrow {\rm{a}} = \hat i + 2\hat j + \hat k$ and $\overrightarrow {\bf{b}} = 2\hat i + 7\hat j + 3\hat k$ . Let ${{\rm{L}}_1}:\overrightarrow {\rm{r}} = ( - \hat i + 2\hat j + \hat k) + \lambda \overrightarrow {\bf{a}} ,\lambda \in {\bf{R}}$ and ${{\rm{L}}_2}:\overrightarrow {\rm{r}} = (\hat j + \hat k) + \mu \overrightarrow {\rm{b}} ,\mu \in {\bf{R}}$ be two lines. If the line ${{\rm{L}}_3}$ passes through the point of intersection of ${{\rm{L}}_1}$ and ${{\rm{L}}_2}$ , and is parallel to $\vec a + \vec b$, then ${{\rm{L}}_3}$ passes through the point :