Question on wavelengths?

Two boats X and Y, 100m apart on a lake, each contain a fisherman. Waves from a ping speed boat travelling in the direction XY p boat X first and then p boat Y. The fisherman in Y notices that when his boat is on the crest of a wave, boat X is in a trough with one crest between the two boats. He also notes that each wave crest takes 4.0 secs to travel from X to Y. Calculate the wavelength, speed and frequency of the water waves.