Finding the population mean from a sample

For a quiz, the question I was given is "Estimate the mean weekly gross sales for all stores that spend $800 on direct mail advertising (Independent variable 1), $1200 on newspaper advertising (Independent variable 2), and $2000 on television commercials (Independent variable 3).

Attached is the regression analysis we were given, which takes into account 25 stores.

Can someone please explain what the best way to calculate this is, because I have absolutely no idea.


Omega Contributor
Make a linear combination of those terms, so y = bo + x1(800) + x2(1200) + x3(2000). Is this something you have covered in your course?