3. Andrea, Beatrice, Chiara, Davide, Enea, and Federico are very good friends. Their average age is 14 years. If they are joined by three of Enea's friends, the average age of the entire group becomes 16 years. What is the average age of the three friends of Enea?
(A) 16
(B) 20
(C) 19
(D) 17
(E) 18
Problem 3. The answer is $\mathbf{( B )}$.

Let's call $a, b, c, d, e, f$ the ages of the six friends whose average is 14 years, and $g, h, i$ the ages of the other three friends of Enea. We know that $a+b+c+d+e+f=14 \cdot 6$ and that $a+b+c+d+e+f+g+h+i=16 \cdot 9$, so $\frac{1}{3}(g+h+i)=\frac{1}{3}(16 \cdot 9-14 \cdot 6)=20$.

(Problem proposed by S. Monica)