Have you learned about “unit rates” yet ?
That’s what you need to use to answer this one.

Mrs. Brown’s homeroom:

                     (72 subscriptions) / (24 students)

                 =    (72 / 24)  subscriptions/students

                 =     average of 3 subscriptions per student

Mrs. Garcia’s homeroom:

         (98 subscriptions)  /  (28 students)

     =      (98 / 28)  subscriptions/students

     =      average of 3.5 subscriptions per student

Mrs. Garcia’s homeroom sold more subscriptions PER STUDENT .