Answer
$$5$$
Work Step by Step
Let us consider that a vector $v$ is given by: $v=pi+qj$
The magnitude of a vector can be determined using the formula
$||v||=\sqrt{p^2+q^2} (1)$
We will use the formula (1) to obtain:
$||v||=\sqrt{(3)^2+(-4)^2}\\
=\sqrt{9+16}\\
=\sqrt{25}\\=5$
