EXCEL HELP

I am a teacher. I have a list of all the students in the freshman class and I am trying to calculate their GPA. Problem is that each students grade in one class is listed as a line item. Also not all students have the same number of classes. Some may have 4 some my have 5 and some may have 7. It just depends. I did a VLOOKUP to convert their letter grades to numberical grades on a 4 point scale. What I am having a hard time with is coming up with a simpler way to average each students GPA without having to average all 400 students in the class. Thanks so much for any help!!!

Here is an example of the first few students...

First Name Mark
SamanthaA 4
SamanthaB 3
SamanthaC 2
SamanthaC 2
SamanthaC 2
SamanthaD 1
SamanthaD 1
Alejandro A 4
Alejandro B 3
Alejandro F 0
Alejandro F 0
Sarah A 4
Sarah A 4
Sarah A 4
Sarah B 3
Jonathan A 4
Jonathan A 4
Jonathan B 3
Jonathan B 3
Jonathan B 3
Jonathan B 3
Jonathan C 2