Yeah,
that's what Pat meant.
What happens when you run this:
SELECT [MAT Cobros].NOMBRE, [MAT Cobros].[Nº PAX], [MAT Cobros].CUIDAD, [MAT Cobros].ENTRADA, [MAT Cobros].MATENT, [MAT Cobros].SALIDA, [MAT Cobros].MATSAL, nz([matent],0)+nz([matsal],0) AS MATTOTAL
FROM [MAT Cobros];
RV