If the lines $x=1+s,\:y=-3-\lambda s,\:z=1+\lambda s$ and $x=t/2,\:y=1+t,\:z=2-t$ with parameters $s\:and\:t$ respectively, are coplanar, then $\lambda=?$

Question

$\begin{array}{1 1}\large(a)\:\:0\:\:\:\qquad\:\:(b)\:\:-1\:\:\:\qquad\:\:(c)\:\:-\large\frac{1}{2}\:\:\:\qquad\:\:(d)\:\:-2. \end{array}$</p