To add a little more to T.K.'s answer, you probably want to go back and review the slides from
Day32-More Dictionaries and Functions
Look for the part about "Counts of Majors", where we did a similar task, involving counting how many students had each major.
(If you want to re-watch the class video where we code that part in Thonny and discuss the code in more detail, the MP4 file is attached to your Google Calendar event from last Wednesday (4/28).