Chapter 8, Problem 29RE

In Problems $29$ and $30$, the vector $\text{v}$ is represented by the directed line segment $\stackrel{\to }{PQ}$. Write $\text{v}$ in the form $\text{a}\text{i+b}\text{j}$ and find $\Vert \text{v}\Vert$.

$P=\left(1,-2\right);Q=\left(3,-6\right)$.