Inventory System Problem Plss Help!!!

I create a inventory system!the data input in Release materials form!subtract the total Qty Remaining in inventory system! the data input in Delivery Form! is add to the total Qty Remaining! delivery Form + Total Qty Mat in Inventory Total Qty Mat in Inventory - Released Form i dont know how to subtract and add data daily in inventory system!Total Qty materials!!! the program if you encode d data in Release Form the program is automatic subract in the inventory and also the delivery form!!!but i have a problem data data is a running data everyday!!!how can i do? Released Form EXAM!!! same day 08/12/2009 # Materials Rel Qty Ctrl#0001 Cement 22 Ctrl#0002 Cement 55 Ctrl#0003 Cement 22 Inventory Form same day 08/12/2009 # Materials End T Inven Rel Qty Remain Qty Ctrl#0001 Cement 250 - 22 228 Ctrl#0002 Cement 228 - 28 200 Ctrl#0003 Cement 200 - 30 170 how can i do that? pls help!!!!