Three lines: $$ \begin{aligned} & L_1: \vec{r}=\lambda \hat{i}, \lambda \in \mathbb{R} \\ & L_2: \vec{r}=\vec{k}+\mu \hat{j}, \mu \in \mathbb{R} \text { and } \\ & L_3: \vec{r}=\hat{i}+\hat{j}+v \hat{k}, \quad v \in \mathbb{R} \end{aligned} $$ are given. For which point(s) Q on $\mathrm{L}_2$ can we find a point P on $\mathrm{L}_1$ and a point R on $\mathrm{L}_3$ so that P , Q and R are collinear ?