Select and Sum?

I’m working on a report header that provides me with the count of a field and then gives me the percentage.
So it counts;
G
L
Y
R
With the code is a number field that corresponds to the code. So I can have the following fields
Code Number
G 12
G 9
L 7
So I would like the code to look for all the “G” and display a “21” because it summed the 12 and 9 in the text box. Can this be done?
Thanks