14. In $\triangle A B C$, $\angle B A C=80^{\circ}, \angle A B C=60^{\circ}, D$ is a point inside the triangle, and $\angle D A B=10^{\circ}, \angle D B A=$ $20^{\circ}$, find the degree measure of $\angle A C D$.
(Mathematical Bulletin Problem 1142)
14. Let $\angle A C D=x$, then $\angle B C D=40^{\circ}-x$, from $\frac{\sin 10^{\circ}}{\sin 70^{\circ}} \cdot \frac{\sin 40^{\circ}}{\sin 20^{\circ}} \cdot \frac{\sin x}{\sin \left(40^{\circ}-x\right)}=1$, we find that $x=30^{\circ}$.