The following example assumes that there is a form called frmTest, that it
includes a text box named txtTest, that the form is open when the query is
run, and that the text box contains a number when the query is run.
'TestNumber' is the name of a field in the table 'tblTest'.
SELECT [Forms]![frmTest]![txtTest]-[TestNumber] AS MyDeduction,
[Forms]![frmTest]![txtTest]+[TestNumber] AS MyAddition
FROM tblTest;