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A rocket travels from the Earth to Planet Z at a speed of 0.8 c. According to observers on Earth, it takes the rocket 15 years to reach Z.

a) How far is Z from Earth in the Earth's frame of reference? Give the distance in light years.

b) What is time for trip in the rocket's frame? Give the time in years.

c) How far is Z from the Earth in the rocket's frame of reference?

d) While the rocket travelling toward Z, Earth sends a radio message to Z. The radio signal (traveling at the speed of light) passes the rocket on the way. At what speed (relative to the rocket) do the observers in the rocket see the radio signal pass by?