Surface areas of the basic solids

You will write functions for the surface areas of the cone, the cylinder and the hemisphere. Then you will compare four solids and find the one with the largest total surface area.

The idea. The slant height of a cone is $l = \sqrt{r^2 + h^2}$. The total surface areas are $\pi r(r + l)$ for the cone, $2\pi r(r + h)$ for the cylinder and $3\pi r^2$ for the hemisphere.

Your tasks.

1. In slant_height, return $\sqrt{r^2 + h^2}$.
2. In cone_total, return the total surface area of a cone, using slant_height.
3. In cylinder_total, return the total surface area of a cylinder.
4. Set largest to the name in solids with the largest total surface area.