wells0587,
Welcome to Bytes!
To briefly answer your question, the answer is, "Yes, it is possible." However, I would recommend NOT adding that total to your Cards table.
If you have a Cards Table and a Supplies Table, with the Card Index as the Foreign Key in your Supplies Table, there is no need to total the cost and send it back to the Cards Table. Just use the inherent relationship and create a sum of all the supplies in your Queries, Forms and Reports.
This is a basic database principle that prevents future headaches.
Hope this hepps!