Answer:
he earns $500 from the lessons from both groups of students.
Explanation:
To summarize:
There are 14 students in set R (piano students)
There are 10 students in set R (piano students) who are not in set S (saxophone students)
There are 11 students in set S (saxophone students)
There are 14 + 11 = 25 total students in both sets R and S
There are 4 students who are common to both R and S, that are taking saxophone for free
The music teacher will get $280 for the piano students
The music teacher will get $220 for the saxophone students.
So the total he earns is $280 + $220 = $500 from the lessons from both groups of students.