Your question lacks some definition. It can mean multiple things.
It does appear you are talking about fields within a table. This is not a usual practice. You typically do not need to store the calculated result of other fields. If the figure is needed, it can always be calculated from the original figures by using SQL. This saves space in the record & database. Also, if the original figures change so must you update the calculated field. If you insist on doing this, you need to do so using an SQL Update statement. This is usually not done in the query section but rather from the main Base screen menu
Tools->SQL.... The exact SQL needed depends upon the database you are using (not stated in question).
If you are talking about doing this on a form for display purposes, you can accomplish this with either a query in a sub form or by using a macro. With the query process the total would only be present on previously entered records while the macro could display the total immediately.
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