Vector Algebra: JEE Main 2011 Mathematics question

Let $\overrightarrow a$, $\overrightarrow b$, $\overrightarrow c$ be three non-zero vectors which are pairwise non-collinear. If $\overrightarrow a+3 \overrightarrow b$ is collinear with $\overrightarrow c$ and $\overrightarrow b+2 \overrightarrow c$ is collinear with $\overrightarrow a$, then $\overrightarrow a+\overrightarrow b+6 \overrightarrow c$ is :