6. A circle with diameter $A B$ intersects segments $A C$ and $B C$ at points $M$ and $N$, respectively, and the length of segment $M N$ is equal to the radius of the circle. Find the area of quadrilateral $A B N M$, given that $A C=12$ and $B C=8$.

![](https://cdn.mathpix.com/cropped/2024_05_06_355bebf291524cccadf1g-11.jpg?height=862&width=899&top_left_y=1057&top_left_x=470)

ANSWER: $18 \sqrt{3}$.