If the lines $x=1+s,\:y=3-\lambda s,\:z=1+\lambda s\:\:and\:\:x=\large\frac{t}{2}$, $y=1+t,\:z=2-t$ where $s\:\:and\:\:t$ are parameters, are $coplanar$, then $\lambda=?$

Question

$\begin{array}{1 1} -2 \\ -1 \\ 0 \\ \large\frac{-1}{2} \end{array} $