Vector magnitude

If $\mathbf{a}=5\mathbf{i}+\mathbf{j}-2\mathbf{k}$ and $\mathbf{b}=2\mathbf{i}+3\mathbf{j}+2\mathbf{k}$, find $|\mathbf{a}-\mathbf{b}|$.

If $\hat{\mathbf{u}}$ is a unit vector, what is $|\hat{\mathbf{u}}|$?

If $\overrightarrow{OA}=4\mathbf{i}+3\mathbf{j}$, $\overrightarrow{OB}=6\mathbf{i}-2\mathbf{j}$ and $\overrightarrow{OC}=2\mathbf{i}-\mathbf{j}$, find $|\overrightarrow{AB}|$ (the length of side $AB$ of triangle $ABC$).