Partial pressures at different heights

You will write a small function that turns a per cent of a gas and a total pressure into a partial pressure. Then you will use it for the oxygen of the air at four heights.

The idea. The partial pressure of a gas is its share of the total pressure.

Your tasks.

1. Finish partial. It gives the partial pressure in mm Hg from the per cent and the total pressure.
2. Finish po2_at. It gives a list with the partial pressure of oxygen (20.95 per cent) at each total pressure of pressures.
3. Set lowest to the lowest partial pressure of oxygen in that list.