Answer:
Constructive interference defination:
''Constructive interference occurs when the maxima of two waves add together (the two waves are in phase), so that the amplitude of the resulting wave is equal to the sum of the individual amplitudes''
Constructive interference occurs at integer multiples of the wavelength of the wave. The lowest incidence occurs at the wavelength.
As we know,
wavelength * frequency = velocity
wavelength = v/f
= (343 m/s) / (220 1/s)
= 1.56 m