Answer:
4.(615384)Hz
Explanation:
Firstly, let's take a note that the speed of light is much higher than 30m/s, on the other hand visible light has wavelengths measured in nanometers, so I assume we're just supposed to assume the values in the question for the purpose of solving it.
If a wave moves through a point with speed v and has wavelength l, In each second we observe v/l cycles - and cycles per second is the frequency!
F = 30m/s / 6.5m = 4.(615384)/s = 4.(615384)Hz
