Change two tables from entry in another table

[lisbet]

I'm a student on work placement and I'm having a few problems with Access.
I need to decrement the fields in two tables by the amount entered into another table.
The tables are Stock and Batches. Stock is for batches previously made and held in stock and batches is for batches being made that day. They both have fields for a unique batch number and an amount and the batch number is only present in one of the tables at any one time.
I have a table for orders being placed to be linked to batches being sent out. This table is called orderLink and has fields for the batch number of the product and the amount being ordered.
Can I run a query to subtract the amount entered into the orderLink table from eiother the stock or batches table depending on where the batch number is present.
Please help because I don't know if this is possible and if it is where to start.
Thankyou