The answer depends on what you are doing with it.
Let's suppose you want the query to return two values, the [Interest Value] and a calculated field called [Gross Interest Value] which is .8 * [Interest Value]
The left column would be
Code:
FIELD [Interest Value]
TABLE [tbl_Master_Tax]
The right column would be
Code:
FIELD [Gross Interest Value]: 0.8 * [tbl_Master_Tax].[Interest Value]
TABLE (leave blank)
Now, as written, that query isn't good for anything much, because you can't related it back to any data. About all it will be useful for is calculating the Sum. You could get the sum easier, with the following SQL:
Code:
SELECT sum(0.8*[Interest Value])
FROM tbl_Master_Tax;
The 0.8 could be inside or outside the sum, and you'd get the same mathematical result.