Microsoft Access query formula for an inventory out come

[Luddy]

Need Microsoft Access query formula for an inventory out come?
I have in my query “part number”, “Date”, “Quantity order”, “Quantity in stock”


Sample
Part number--- -date---------- Qty order------ Original in stock------- remaining in stock
(1) 841970----- 11-21-13---------- 25-------------------- -150------------------- (125)
(2) 841970----- 12-2-13------------ 25 ---------------------150------------------- (100)
(3) 841970 -----12-5-13 ------------25--------------------- 150-------------------- (75)
(4) 747120 -----12-30-13--------- 500 ---------------------300------------------- (300)
(5) 841970------1-5-14--------------25-----------------------150-------------------- (50)
(6) 841970------ 2-2-14------------ 50---------------------- 150--------------------- (0)
How do I create a formula to get my remaining in stock to decrease every time I add an order?

[June7]

Review http://allenbrowne.com/AppInventory.html

Have you looked at the Inventory database templated published by MS?