If $\overrightarrow a\:and\:\overrightarrow c$ are unit and collinear vectors and $|\overrightarrow b|=6$, then $\overrightarrow b-3\overrightarrow c=\lambda \overrightarrow a,$ if $\lambda=?$

Question

$\begin{array}{1 1} -9,3 \\ 9,3 \\ 9,-3 \\ 3,-3 \end{array}$