A Spaceship Is Going Away from Earth with a Speed

Multiple Choice

A spaceship is going away from Earth with a speed 0.28c. A passenger in the spaceship measures his heartbeat as 72 beats per minute. How many beats per minute are observed in the telemetry radio signals received on Earth? Note that, in addition to time dilation, one must take into account that the signals of successive heartbeats have to travel longer distances because the spaceship is moving away (Doppler Effect) .

A) 75
B) 96
C) 54
D) 69
E) 100