**HINT**
How much material used is determined the by the area of the container.
Area of the bottom + area of the side
$$=\pi r^2 + 2\pi rh = \pi r^2 + \frac{2a^3}{r}$$
**HINT**
How much material used is determined the by the area of the container.
Area of the bottom + area of the side
$$=\pi r^2 + 2\pi rh = \pi r^2 + \frac{2a^3}{r}$$