My suggestion would be to create a consolidated database, that you copy all the tables for the others to by using cut and paste.(This will create a static copy, if you want it dynamically linked, you need to use a different process) You could then create a query to do your sums based on all the data tables.
If you do want a dynamic link, create a new database and right click on the table area. You should be presented with a link tables option. Select that and find each of your databases in the file selection. You can link your other database table to the consolidated one using this. Then create your sum query this way.
Hope this helps.