Excel 2007 : Conditional Formatting Based on Changing Benchmark?

I'm making a sheet to track if students are on-pace with their work. The first column lists how many articles (running total) they should have complete each week. So if they look at week 10, they know they should have 20 articles done.

Each column is then the student's running total, entered on the Friday of each week. So for week 10, some students will be below, at, or above the expectation of 20 articles total. I'd like to color code it red, yellow, or green based on if the student is below, at, or above the goal for that week.

Since the goal or number the conditional formatting is being compared to changes each week (20 week 10, 22, week 11, etc.), I'm not sure how to set it up properly. It keeps returning an error that conditional formatting can only be compared to a single cell. How can I fix this so the columns are being compared over time? See attached-