Question

Waves are observed passing under a dock. Wave crests are 8.0 meters apart. The time for a complete wave to pass by is 4.0 seconds. The markings on the post submerged in water indicate that the water level fluctuates from a trough at 6.0 meters to a crest at 9.0 meters. What is the period of the wave?

Answer 1

period of wave is time takes wave to pass the fixed point.
you have been said that it's 4s, that's the answer
T = 4s