First of all although there is no image described at the bottom, attached that fits perfectly with the experiment carried out.
From this perspective to solve this problem we must be guided by the kinematic equations of angular motion.
By definition we know that through the number of Notches it is possible to identify the total angular displacement in revolutions, that is to say


The kinematic equations of motion tell us that speed (in this case that of light) can be expressed as

Where
d = distance
t = Time
Since the light has a round trip we have to


Our values are given as


From these same equations we have then that

Replacing with the two previous values found



Therefore the minimum angular speed of the wheel for this experiment is 114.304rad/s