Astronomer On Earth Observes

An astronomer on Earth observes a meteoroid in the southern sky approaching the Earth at a speed of 0.800c. At the time of its discovery the meteoroid is 20.0 ly from the Earth. Calculate
(a) The time interval required for the meteoroid to reach the Earth as measured by the earthbound astronomer,
(b) This time interval as measured by a tourist on the meteoroid, and
(c) The distance to the Earth as measured by the tourist.

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