Help!

I have a 3 page spreadsheet that I need to maintain. The first page is a
table that basically has part number, attribute A, attribute B and starting
inventory level. Attributes A and B are unrelated to this exercise and can be
ignored.

Page 2 has all of the customer orders, the only 2 cells that matter are are
part number and quantity.

On page 3 I would like to have a list with each of the part numbers and the
current inventory level.

Theoretically, I need a formula like a vlookup on page 3 that will look at a
value (the part number), find the initial starting inventory from page one,
and then subtract all of the quantities for that part on page 2. The net
number should be inventory on hand.

This sounds simple but I am racking my brain trying to figure it out.


The second page