1971 AHSME Problem 10

Each of a group of 50 girls is blonde or brunette and is blue eyed of brown eyed. If 14 are blue-eyed blondes, 31 are brunettes, and 18 are brown-eyed, then the number of brown-eyed brunettes is

\textbf{(A) }5\qquad \textbf{(B) }7\qquad \textbf{(C) }9\qquad \textbf{(D) }11\qquad \textbf{(E) }13

Full credit goes to MAA for authoring these problems. These problems were taken on the AOPS website.