Need some Excel help please!

Hello -
I have some spreadsheets containing employee roster information. It's confusing because people from
different areas are mixed up under supervisors from other areas, so counting and tabulating some of the
information is a real pain! I added a column to designate with a single letter the areas where people work. Now I need to figure out how to write a formula that will average the months of service by area, if the letter in the new column is A or B or C or whatever. Any clues?
Thanks much!

gran