Three SQL TABLES Payment, Appointment, Doctor Find average salary of each patient : Create Table Doctor(
	doctorID varchar(50) Primary key,
	doctorFName varchar(50),
);

Create Table Appointment(
	appID varchar(50) Primary Key,
	doctorID varchar(50) Foreign Key References Doctor(doctorID),
);

Create Table Payment(
	paymentID varchar(50) Primary Key,
	paymentAmount int,
	appID varchar(50) Foreign Key References Appointment(appID),
);

paymentAmount is also known as payment for each appointment

How can i get the average payment amount of each doctor?