The blood count calculator

A blood report gives counts in each microlitre. You will find the plasma, count the cells in a sample and flag a count that is outside its usual range.

The idea. One millilitre is $1000$ microlitres. The usual range for platelets is $150000$ to $400000$ in each microlitre.

Your tasks.

1. Finish plasma_litres. It gives the volume of the plasma, from the volume of blood and the haematocrit in per cent.
2. Finish cells_in_sample. It gives the number of cells in a sample, from the count in each microlitre and the sample in millilitres.
3. Finish flag. It gives "low", "normal" or "high".