How to exclude data in table?

Hi there I have 2 tables with account numbers.

1st table is named 30 dy ltr & the second is AFS Bankrupt Loans(3).

the 1st table picks up accounts that are 30 days past due, the 2nd one picks up all loans that are in bankruptcy. Sometimes I get accounts that are 30 days past due & that same account is in the bankruptcy table. I would like to exclude that loan from my query.

I have no idea how to start on this... any ideas???