please help me and give an explanation

Explanation:

The moon orbits the Earth once every 27.322 days. It also takes approximately 27 days for the moon to rotate once on its axis. As a result, the moon does not seem to be spinning but appears to observers from Earth to be keeping almost perfectly still. Scientists call this synchronous rotation

resonant frequency

the answer is f1 and d2 because if you put equal force on those two points the beam would balance trust me on this