\vec{d}(t) = \vec{P} - \vec{r}(t) = \begin{pmatrix} 3 - (1 + 2t) \\ -1 - t \\ 2 - (-3 - t) \end{pmatrix} = \begin{pmatrix} 2 - 2t \\ -1 - t \\ 5 + t \end{pmatrix}