I've removed the logon details from your post. These are public forums, you should never post logins here. I suggest you change your password, as even though I removed the password, Google probably has the page cached by now.
I'm still not sure what you are trying to do. What are you wanting to subtract from?
Typically any sort of stock control, you would have at least three tables - one for "stock" (with the product id / name, and the current stock count), one for "sales" and one for "purchases", where the sales and purchase forms have PHP plugins that calculate and update the stock levels.
So I'm not sure how / what you are trying to do with just that one table you showed us.
-- hugh