Welcome to the PICAXE forum.
It would be useful to know what specific help you need; how to build a number to use or store, or how to have such a number stored, whether you need to know the basic principles or help with actually doing that.
Obviously with coursework people won't be wanting to do that for you and I doubt you would want them to do that either, just need help with the bits you haven't got to grips with yet. Perhaps you could briefly explain what you do have working and what you need to take it to the furtherl.
I guess that's all in the code you have, but it will help people understand what you have without having to figure that out for themselves.
There are a number of discussions on the forum about handling keypads and alarm codes and sequences which would be worth searching for. One which may be useful is -
http://www.picaxeforum.co.uk/showthread.php?28307-KeyPad-accept-reject-input&p=292585