How many people are directors of both charities A and B

How many people are directors of both charities A and B?

(1) Charity A has 16 directors and Charity B has 9 directors.

(2) 18 directors attended a joint meeting of the directors of Charity A and Charity B, and not one director was absent from the meeting.

COLUMNS: Charity A / NOT Charity A / Total

ROWS:
Charity B
NOT Charity B
Total

DESIRED QUANTITY is the TOP LEFT.

(a)
bottom left = 16
top right = 9
insufficient.

(b)
middle square = 0
bottom right = 18
insufficient.

(together)
if you have both statements, you can fill in the whole grid.
7 2 9
9 0 9
16 2 18
so, top left = 7.
sufficient.

Ans : C