physics question

(a) path difference = (20.5 - 20) m = 0.5 m
wavelength of sound = 330/2500 m = 0.132 m
hence, path difference = 0.5/0.132 wavelengths = 3.79 wavelengths
There is neither constructive nor destructive interference occur at P


(b) Let M be the rate of water flow in kg/minute
Heat absorbed by water in 1 minute
= M x 4200 x (14 - 6) J/minute = 33600M J/minute

hence, 6.72 x 10^9 = 33600M
i.e. M = 6.72x10^9/33600 kg/minute