A graph of displacement against distance for a wave passing through water is given below.
Wavelength is the distance covered by a full cycle of the wave, usually measured from peak to peak, or trough to trough. The distance between 2 peaks is 8 m. The wavelength of the wave is 8 m.
Amplitude is the maximum displacement of a point of a wave from its rest position.
The maximum displacement is 2.5 mm.
The amplitude of the wave is 2.5 mm.