Mysql query for getting result !!

Can anyone help me on this please??
I am trying to make a stock exchange system based on mysql database using vb...

So i am stuck on :
my sql table : inProduct, OutProduct and Stock...
inProduct cells > id,prodName, quantity, units, date
OutProcust cells > id,prodName, quantity, units, date
Stock cells > prodName, quantity,units

So i want query to show on listview... with this i have 3 listview of this tables to show data...
now i want query to show Stock in Stock listview that will result like > Quantity of inProduct - Quantity of OutProduct = Stock quantity...
100 - 50 = 50...
So when i add inProduct it will add with Stock,,, and when i add OutProduct it will minus from stock... then show listview...

Please i need this mysql query for vb.net
And please let me if you cannot understand what i am asking for then i will give you codes for the problem...

It will be great pleasure to me if anyone help me on this purpose... Thanks in advance....