A wave passes the dock every 5 seconds and reaches a height of. 5 meters and a wavelength of 2 meters. find the wavespeed

We don't care about the height of the wave.

We're only interested in its period and wavelength, because

wave speed is the product of frequency and wavelength.

Period = 5 seconds

Frequency = 1/period = 1/5sec = 0.2/sec = 0.2 Hz.

Speed

= (frequency) x (wavelength)

= (0.2 Hz) x (2 m) = 0.4 m/s.