Let \( \vec{a}= \hat{\imath}+2\hat{\jmath}+3\hat{k} \), \( \vec{b}=2\hat{\imath}+3\hat{\jmath}-5\hat{k} \) and \( \vec{c}=3\hat{\imath}-\hat{\jmath}+\lambda \hat{k} \) be three vectors. Let \( \vec{r} \) unit vector along \( \vec{b}+\vec{c} \). If \( \vec{r}\cdot \vec{a}=3 \), then \( 3\lambda \) is equal to :
