permit_zone

Hi All Am new to MS Access and am trying to build a database and some forms, and source the fields in the form to the tables in the database. While doing this, I have an issue where am struck and can't find any help so far any where. Hope I'll get my issue resolved from here. I have a form that has two combo boxes(combo01 - 'TOWN_CD' & combo02 - 'REV_CD') and a text box(APPLCBL_RT). Now I want the text box to pop up the 'applicable rate' amount from the values I choose from the two combo boxes, Town Code and Rev Code. The 'applicable rate' will be picked from the 'Rate Table' Now there is a small catch in this. The 'Rate Table' has 'Rev Codes ' and 'County Codes', not 'Town Code'. But the 'Town Table' has Towns and their corresponding County's. Now what am looking for is, When I pick a 'Town' form combo01 and 'Rev Cd' from combo02, I need a code that will pick corresponding 'County' from 'Town Table' and should pull the 'applicable rate' from this 'County' and 'Rev Cd' from the 'Rate Table'. Hope am clear on my question. If not please let me know. Also I need to know where and how to apply those logics. Thanks in Advance.