Combine functions?

[~suky~]

I'm am in real stress right now, as i really need help with my excel
coursework.

I'm doing a stocking system with Excel, i created 3 worksheets - a
sales update, stock update, and the stock level database. So each time
a product is sold, so i would just type in the cat. number of the
product and the quantities of it been sold, and this is automaticly
been found and reduce on my stock level database - which include the
cat. number and quantities and other details of each product. (Notice
that the cat. number would be different everytime...)

I'm struggling to set up a function which allow me to look-up the
particular product in stock database AND reduce the sold quantities of
this product where i have entered perivously in the sales update sheet.


Is there a combine functions that i could use? I'm thinking of using
VLOOKUP and copy&Past special in the first place, but then it's useless
- as the cat nubmer would be different each time! it's not always in the
same cell and row!

Could somebody please help me with this?!

Thank you So much!!!!!!

Suky
xxxxx