Write the SQL code to find the average charge by the family medicine physicians

We need to write the script to find the average charge of physicians who specialize in "family medicine.

But i’m confused on how to write this because when we look at the appointment table, where we find the appointment_charge, it only gives us the physician_ID. How to link that to the specialize table. Can anyone help me solve this problem?

This link below contains the diagram, tables and question. I am stuck at number 13. Take a look, it will make more sense 🙂 >>>>