Answer
$7$
Work Step by Step
Let us consider that vector $v$ is given by:
$v=pi+qj+rz$
The magnitude of a vector can be determined using the formula
$||v||=\sqrt{p^2+q^2+r^2} ...(1)$
We will use the formula (1) to obtain:
$||v||=\sqrt{(3)^2+(-6)^2+(-2)^2}\\
=\sqrt{9+36+4}\\
=\sqrt{49}\\
=7$