Simple Question on Addition

I searched the discussion groups for the answer to what seems to be a simple
question, but found nothing. I have a group by query with three columns:

itemNo
Debits
Credits

The query is grouped on the first column, itemNo.

I want to add the Debit column to the credit column and show the result in a
third field, Total. For each record, the Debit column contains currency
amounts. The Credit column contains either negative currency amounts or is
null.

Here is my nonfunctioning SQL. When I run the query, the Total column is
blank for every record.

SELECT eBayFees_lastMonth.[Item number], Sum(eBayFees_lastMonth.Debits) AS
SumOfDebits, Sum(eBayFees_lastMonth.Credits) AS SumOfCredits,
Sum([eBayFees_lastMonth.Debits] + [ebayFees_lastMonth.Credits]) AS Total
FROM eBayFees_lastMonth
GROUP BY eBayFees_lastMonth.[Item number]
ORDER BY eBayFees_lastMonth.[Item number];

Any ideas?

Thanks,
GwenH