jmc

We know that $y=-6$ from the given information. By the distance formula, we have the equation $\sqrt{(x-8{)}^2+(-6-3{)}^2}=15$. Solving, we have $$\begin{array}{rl}\sqrt{(x-8{)}^2+(-6-3{)}^2}& =15\\ x^2-16x+64+81& =225\\ x^2-16x-80& =0\\ (x-20)(x+4)& =0\end{array}$$Thus, $x+4=0$ or $x-20=0$, so $x=-4$ or $x=20$. $x=-4$ by the given conditions. Thus, our point is $(-4,-6)$ and is a distance of $\sqrt{(-4{)}^2+(-6{)}^2}=\sqrt{52}$ units from the origin. $n=\boxed{52}$.