Answer:
50 Hz
Explanation:
For those who like equations:
Velocity = frequency × wavelength
For those who like a more intuitive explanation:
Frequency represents how many waves can go through a single point in 1 second. If you have a wave traveling 10 meters per second, and for each wave the length is 0.2 meter, then you know that there are 50 waves stacking together to reach a total length of 10 meters. So, in 1 second, 50 waves can pass, and therefore the answer is 50 Hz
