The field should only accept values from 39 until 47.
It can be empty.
It should be editable on the admin member edit page.
It should be visible on the public user profiles.
This hint is about the third bullet (surprise): It's a field for the shoe size.
In the previous step you should have added an IntegerField to the Profile model. However, if you followed the hint, you haven't given it a name yet. Give the field a sensible attribute name and take a look at the documentation about adding a verbose name. Don't forget that concrexit is multilingual, so you might need the documentation for translations as well.