How to us the IF function based on multiple cells

[gloriousglenn]

I always find it hard to describe the problem I have in a few words for the "Title"!!

Anyway, here's my issue...
I have four columns for calculating annual bills. Some bills are paid bi-weekly, some monthly, and some bi-annually. I have an "Annual" column I would like a formula that says if the bi-weekly column has a number in it, multiply it by 26, but if that is blank and the monthly column has a number in it, multiply that number by 12 and if the bi-annual column has a number in it, multiply that by 2. There will never be a case where more than one column will have a number in the same row.

In the attached, you will see that I know how to use the IF function for one cell, but I want it to auto-calculate no matter which of the three columns I put a number into.

Thanks in advance.
Glenn