Answer: A crest with an amplitude of 9 will form.
Explanation:
From super position principle, we know that when two waves move in same medium meet, then the net amplitude of the super imposed waves is sum of amplitudes of individual waves.
A constructive superposition takes place when crest meets crest and crest is formed of higher amplitude or trough meets trough and forms trough of higher amplitude. A destructive superposition takes place when crest of one meets trough of other -a crest or trough can form depending on the larger amplitude of either.
In the given situation, crest of wave X meets crest of wave Y. The amplitude of the super imposed wave would be = 5 + 4 = 9 and a crest would form.
