[Geometry]
Problem: The sum of the interior angles of an $n$-gon equals the sum of the interior angles of a pentagon plus the sum of the interior angles of an octagon. Compute $n$.

Solution: Using the angle sum formula, $180^{\circ} \cdot(n-2)=180^{\circ} \cdot 3+180^{\circ} \cdot 6=180^{\circ} \cdot 9$. Thus $n-2=9$, and $n=11$.

Final answer: 11