Yes just create a table with a KEY and the average, may be like:
Autonumber(Field1&Field2&Field3) as KEY,
Avg(Sales) as CompanyAvgSales
resident <> Group by Field1, Field2, Field3;
Assuming Field4 (which is not there in the composite key) is your sale rep field.
Now create a similar key in your transnational table, it should work.