I'm trying to find a way to remove inventory when an order is sold, other than manually changing the numbers. I have a form set up to add new orders to the bottom of the sheet. I need a formula to automatically remove the inventory items from each line in the Sold column. Example:

Customer #1 bought 5 items of my Stock #2. I need it to change the 0 in the Sold column to 5 on line 3.

It also needs to be able to update when another order is added. Example:

Customer #3 bought 35 items from Stock #2. So now the 5 would be changing to 40 (in the Sold column on line 3).