\[\mathbf{Схематический\ рисунок.}\]
\[Решение.\]
\[S_{\text{MKN}} = 75\ см^{2};KN = 15\ см;\]
\[\angle K = 30{^\circ}:\]
\[S_{\text{MKN}} = \frac{1}{2}MK \bullet KN \bullet \sin{\angle K}\]
\[MK \bullet 15 \bullet \sin{30{^\circ}} = 150\]
\[MK \bullet \frac{1}{2} = 10\ \ \ \]
\[MK = 20\ см.\]
\[Ответ:\ \ 20\ см.\]