We are given with the following value:
Velocity = 3.5 m/s
Distance = 4m
We are asked to solve and determine the frequency of the water waves, the solution is shown below:
Velocity = frequency * Distance
Frequency = Velocity / Distance
Frequency = 3.5 m/s / 4m
Frequency = 0.88 Hz
The answer is letter "A" which is 0.88 Hz.