Answer
(a) $600m$
(b) maximum
(c) $200m$
Work Step by Step
(a) The largest possible value for the wavelength of the radio waves is equal to half a wavelength of the radio waves:
$\frac{\lambda}{2}=300m=600m$
(b) We know that when the path difference is equal to one wavelength, then difference is equal to one half wavelength and the waves are out of phase. Thus, the waves produce maximum constructive interference.
(c) We know that next minimum signal occurs when the path difference is equal to one half wavelength.
Thus $450m-150m=\frac{3\lambda}{2}$
$\implies 300m=\frac{3}{2}\lambda$
$\implies \lambda=200m$
