So, here's the question: I'd like to calculate what the number of visitors "should" be based on the number of stores given the correlation. For example, metro area X with 10 stores had 25,000 visitors...how many "should" they have had given the data?

What's the best...if any...way to do this?

And I should also say that this isn't for homework, but it didn't seem to fit anywhere else and since I need to figure it out for a work project, I guess it may as well be homework.