Physics Help?

A small mirror is attached to a vertical wall, and it hangs a distance of 1.54 m above the floor. The mirror is facing due east, and a ray of sunlight strikes the mirror early in the morning and then again later in the morning. The incident and reflected rays lie in a plane that is perpendicular to both the wall and the floor. Early in the morning, the reflected ray strikes the floor at a distance of 3.18 m from the base of the wall. Later on in the morning, the ray is observed to strike the floor at a distance of 1.25 m from the wall. The earth rotates at a rate of 15.0˚ per hour. How much time (in hours) has elapsed between the two observations?