Answer
$y = \pm 12 $
Work Step by Step
$\cos{\theta} = \dfrac{x}{r} = \dfrac{5}{13}$
$\therefore x = 5 \hspace{20pt} r = 13$
$r^2 = x^2+y^2 \\ y^2 = r^2 - x^2 \\ y = \pm \sqrt{r^2-x^2} \\ = \pm \sqrt{(13)^2-(5)^2}$
$\boxed{y = \pm 12}$