Two vector $$\vec{a}=a_1 \hat{i}+a_2 \hat{j}+a_3 \hat{k} \quad$$ and $$\vec{b}=b_1 \hat{i}+b_2 \hat{j}+b_3 \hat{k}$$ are collinear if:

The magnitude of the vector $$6 \hat{i}-2 \hat{j}+3 \hat{k}$$ is :