3.20: Rectangle inside a circle with external segments

The diagram shows a circle, centre $O$, radius $12\text{ cm}$, and a rectangle $ABCD$. The diagonals $AC$ and $BD$ intersect at $O$. The sides $AB$ and $AD$ of the rectangle have lengths $6\text{ cm}$ and $4\text{ cm}$ respectively. The points $M$ and $N$ lie on the circumference of the circle such that $MAC$ and $NDB$ are straight lines.