Write vector and Cartesian equations without dividing by zero

Find a vector equation and cartesian equation of the following lines:

(a) passing through the point with position vector $7\mathbf i+2\mathbf j-4\mathbf k$ and parallel to to $\mathbf i-3\mathbf j+\mathbf k$

(b) passing through the points $(2,-2,1)$ and $(0,4,9)$

(c) passing through the point with position vector $7\mathbf i$ and parallel to the line $\mathbf r=(2-p)\mathbf i+p\mathbf j+5\mathbf k$.