Question

For an ocean wave that has the crests 6 m apart and passing a boat every two seconds, calculate the speed of the wave.

Answer 1

I guess the boat is anchored?

6 m/2 s = 3 m/s

Note:
That is the speed of the crest or "phase velocity". The speed of the group of waves, the "group velocity" is (1/2) of that if they are deep water waves. Energy is propagated at the group velocity. In real life the front wave is constantly disappearing and being replaced by one behind it.
http://oceanworld.tamu.edu/resources/ocng_textbook/chapter16/chapter16_01.htm

Answer 2

A human ear can hear as low as 15.6 Hz. If the speed of sound in the air was measured to be 340.5 m/s, calculate the wavelength of this wave.