Figure shows a radio-wave transmitter and a receiver, both h = 50.0 m above the ground and

Question:

Figure shows a radio-wave transmitter and a receiver, both h = 50.0 m above the ground and d = 600 m apart. The receiver can receive signals directly from the transmitter, and indirectly, from signals that bounce off the ground. If the ground is level between the transmitter and receiver and a λ/2 phase shift occurs upon reflection, determine the longest wavelengths that interfere(a) Constructively and(b)Destructively.