Two Radio Antennas Are 10 Km Apart on a North-South

Multiple Choice

Two radio antennas are 10 km apart on a north-south axis on high mountain tops at the seacoast.The antennas broadcast identical AM radio signals,in phase,at a frequency of 4.70 MHz.A steamship,200 km offshore,travels toward the north at 15 km/h and passes east of the antennas.A radio on board the ship is tuned to the broadcast frequency.The reception of the radio signal on the ship is a maximum at a given instant.How much later until the next occurrence of maximum reception? (c = 3.00 × 10⁸ m/s)

A) 5.1 min
B) 3.8 min
C) 6.4 min
D) 7.7 min
E) 8.9 min