How to start the process of coming up with the predicted math score?
What you are looking for is a machine learning algorithm. Although the easiest way would be to take the average scores and use that, there are much more accurate ways to make predictive models.

This was the first data science tutorial I did. It's perfect for getting started. Here is it in R and in Python.

If you're looking for a short answer, something you can just look up how to implement, I'd check out Random Forests.