Best way to average numbers across rows and columns

Hello,

What is the best way to average numbers both that span across both rows and columns?

I have a table that holds student names (y-axis), tests they take (x-axis), and their scores. I need to average the student's scrore for all tests and also average the test scores for all students.

How should I go about saving the data so I can then do some maths on it?

Thanks.