Here's what I ended up with, the query will actually use 2 table to eventually put more criteria. Seems to work OK.

SELECT Invoice.amount, Invoice.invoice, Invoice.file_num, Invoice.date;
FROM openclose!nrcs INNER JOIN openclose!invoice ON Nrcs.file_num = Invoice.file_num;
WHERE invoice.file_num + dtos(invoice.date) in (SELECT invoice.file_num + dtos(max(invoice.date)) From INVOICE GROUP BY file_num);
GROUP BY invoice.file_num

Thanks for the help.