5. On the sides $A B$ and $B C$ outside the triangle $A B C$, two equilateral triangles $A B M$ and $B C N$ are constructed. Points $P, Q$, and $R$ are the midpoints of segments $A B, M N$, and $B C$ respectively. Find the area of triangle $P Q R$, if the length of side $A C$ of triangle $A B C$ is 8.
Answer: $\quad S_{P Q R}=4 \sqrt{3}$.