If $\hat i -3 \hat j +\hat k$ and $\lambda \hat i+ 3 \hat j$ are coplanar, then $\lambda$ is equal to :

Question

$$\begin {array} {1 1} (a)\;-1 & \quad (b)\;\frac{1}{2}\\ (c)\;\frac{-3}{2} & \quad (d)\;2\end {array}$$