Right Before Takeoff,a Passenger on a Plane Flying from Town

Right before takeoff,a passenger on a plane flying from town A to town B synchronizes his clock with the clock of his friend waiting for him in town B. The plane flies without interruption for 5.00 hours at a constant velocity.The moment the plane touches the ground the two friends check simultaneously the indication of their clocks.The difference between the readings of the clocks B and A is 7.56 ns.Ignoring any effects of acceleration,the constant velocity of the plane was

A) 178 m/s.
B) 354 m/s.
C) 243 m/s.
D) 328 m/s.
E) 275 m/s.