In a group of 36 persons, a total of 16 take tea while 9 take tea but not coffee. How many persons in this group take coffee but not tea?

In a group of 36 persons, a total of 16 take tea while 9 take tea but not coffee.  How many persons in this 
group take coffee but not tea?
(a) 27
(b) 20
(c) 25
(d) 11

Answer: 20