mysql> select
    -> id, email_address, avg(grade) as avg_Grade from students, grades
    -> where students.id = grades.student_id and students.first_name='Jack' and students.last_name='Johnson';
+-----+------------------------------+-----------+
| id  | email_address                | avg_Grade |
+-----+------------------------------+-----------+
| 257 | jjmuzak@brushfirerecords.com | 95.333333 |
+-----+------------------------------+-----------+
1 row in set (0.00 sec)