Answer
$$36 \pi$$
Work Step by Step
Consider the shell model to compute the volume:
$$V=\int_{m}^{n} (2 \pi) (\space Radius \space of \space shell) \times ( height \space \text{of} \space \text {shell}) dx \\ =
\int_0^{3} (2 \pi) (x) \times [\dfrac{9x}{(x^3+9)^{1/2}}) \space dx$$
Let us consider $a=x^3+9$ and $ da=3x^2dx$
$$V=(2 \pi) \times \int_{9}^{36} (3) \times a^{-(1/2)} da \\=6 \pi \times (2 \sqrt a)]_{9}^{36} \\=36 \pi$$
