Answer:
2.55 Hz
Step-by-step explanation:
The frequency of the wave given it's velocity and wavelength can be found by using the formula

where
c is the velocity of the wave in m/s
is the wavelength in m
From the question
c = 7.9 m/s
= 3.1 m
We have

We have the final answer as
2.55 Hz
Hope this helps you