Conditional Formatting for Multiple Rows

Hello again gang,

Today my problem is with Conditional Formatting. I have a spreadsheet of a couple hundred products, their sales over the last 18 months, and then each product's 18 month average monthly sales.

What I would like to do is format them so if any of the months' sales are below their respective average, that cell/month with be highlighted. Excel told me that I cannot do this for multiple rows at a time, and I don't want to go row by row for this many products.

Attached is a sample file of the first row.