The plane $F$ intersects the $x _ { 1 } x _ { 2 }$-plane in the line $g$. Determine an equation of $g$.
(for verification: $g : \vec { X } = \left( \begin{array} { c } 30 \\ 0 \\ 0 \end{array} \right) + \lambda \cdot \left( \begin{array} { c } 1 \\ - 3 \\ 0 \end{array} \right) , \lambda \in \mathbb { R }$ )