Are you smarter than me? (OPTICS)

A light ray incident on a rotating mirror $M$ is returned to a fixed mirror $N$ placed 22.5 km away from $M$ . The fixed mirror reflects it back to $M$ (along the same path) which in turn reflects the light again along the direction that makes an angle of $27^\circ$ with the incident direction. Find the speed of the rotation of the mirror in revolutions per second.