A fisherman notices that his boat is moving up and down periodically without any horizontal motion.

owing to waves on the surface of the water. It takes a time of 3.00 s for the boat to travel from its highest point to its lowest, a total distance of 0.630m . The fisherman sees that the wave crests are spaced a horizontal distance of 5.80 m apart.

How fast are the waves traveling?

V = f lambda
= lambda / T
= 5.80 /6 = 0.97 m/s

Note that it takes 6 seconds to go from the top of one wave to the top of the next.