Volumes of joined solids

You will write functions for the volumes of a cone, a hemisphere and an ice cream (a cone with a hemisphere on top). Then you will change a volume from cubic centimetres to litres.

The idea. The volume of a cone is $\frac{1}{3}\pi r^2 h$ and of a hemisphere $\frac{2}{3}\pi r^3$. The volumes of joined solids add. One litre is $1000\ \text{cm}^3$.

Your tasks.

1. In cone_volume, return $\frac{1}{3}\pi r^2 h$.
2. In hemisphere_volume, return $\frac{2}{3}\pi r^3$.
3. In ice_cream, return the volume of a cone of height h with a hemisphere on top, both with radius r.
4. In litres, return the number of litres in a volume given in cubic centimetres.