\[Схематический\ рисунок.\]
\[AC = 3\sqrt{3}\ см;\]
\[BD = 4\ см;\]
\[\angle BOA = 60{^\circ}:\]
\[S = \frac{1}{2} \bullet AC \bullet BD \bullet \sin{\angle BOA} =\]
\[= \frac{1}{2} \bullet 3\sqrt{3} \bullet 4 \bullet \sin{60{^\circ}} =\]
\[= 6\sqrt{3} \bullet \frac{\sqrt{3}}{2} = 9\ см^{2}.\]
\[Ответ:\ \ 9\ см^{2}.\]