Brad,
Can you explain a little more about your need? Is there a reason for storing the results of a calculation in the table? What do "A" and "B", etc. represent - tables, field names, numbers, text, what?
Also, what Rick Brandt stated about having a field in a table do the calculation is correct, although there are methods of updating a table with the results of a calculation. In MOST cases, storing the result of a calculation is redundant and considered to be non-normalized table design, however, there are times when it is advantageous to do so.
Post back to this thread and we'll try to help.