Looking for formula for Inventory on Hand

Hi People,

Can anyone help me with formulas for the attached document? The attached document is a inventory, outgoing and incoming file. In column J, I would like to pop up the inventory available when a new item (or row) is entered to last row. The inventory on hand is at tab Incoming material. Both tabs have thousands of rows.
And the second formula I would like to have, would be one that can deduct the quantity taken from tab Incoming material Col A with the first Item at the top, if quantity available in that row does not cover the demand entered in Tab Out Going shipments, then look for next Item in Col A and deduct the balance. Example:


TAB Out going shipments TAB Incoming material

Quantity ITEM Quantity ITEM
48 EM0040026 18 EM0040026 Take the 18
10 EM0040026 Take the 10
50 EM0040026 Take the balance which is 20