Excel Formula question

My apologies if this isn't the right venue for this but...

I'm adding some functionality to an app that automates Excel that someone long gone has written.

I need to calculate the average of a row of numbers (monthly sales totals).

Jan Feb Mar Apr May.... Average
10 15 9

However if not all the months have values like in the example above, then
I only need the average of Jan, Feb, and March.

I would prefer to pass a native Excel function/formula into the .cells(x,x).value property if possible, otherwise if someone can help me out with a sub that I can pass the underlying field values from the database(Access 97) table
to.

The spreadsheets are always created from scratch so I don't think using a prebuilt template is going to be easy to implement as I'm loathe to make any significant changes to the existing code base.

Thanks in advance for any help.
Jack Vinitsky