## Precalculus (10th Edition)

$16$
The magnitude $||v||$ of a vector $v=ai+bj+ck$, can be computed using the formula $||v||=\sqrt{a^2+b^2+c^2}$. Hence, using the formula above gives $||v||=\sqrt{(-6)^2+12^2+4^2}\\||v||=\sqrt{36+144+16}\\||v||=\sqrt{196}\\||v||=16.$