You haven't listed the information in the table, but that's okay :). I believe I can still help you.
To find the average score on the test for this group you would have to add up all the test scores listed in the chart, then divide that sum by the number of people in the group.
Here's an example;
I'll make a list of people with some test scores
Jimmy- 80
Andrea- 44
Samuel- 15
Jerica- 65
To find the average of their scores, I'll first add up their points:
80+44+15+65 = 204
Once I've calculated my sum, I will divided that sum by the number of people who took the test. In this case it's 4 different people, so :
204÷4= 51
So in my made up scenario the average score in my group was 51.
Now you can apply this process into your problem.
(Hope this helps :). Please let me know if you need more help on this problem)