64. Inside the square $A B C D$, a point $M$ is taken such that $\widehat{M A B}=60^{\circ}, \widehat{M C D}=15^{\circ}$. Find $\widehat{M B C}$.
64. Construct an equilateral triangle $A B K$ on $A B$ inside the square. Then $\widehat{K A B}=60^{\circ}, \widehat{K C D}=15^{\circ}$, i.e., $K$ coincides with $M$. Answer: $30^{\circ}$.