Special Relativity

A space vehicle is accelerated to 0.8 of light speed as it leaves the solar system. One year later a stationary extraterrestrial watches the vehicle pass and measures the length of the vehicle to be 12 m. What is the length of the vehicle on earth before it begins its trip?

a)   7.2 m

b)   12 m

c)   18 m

d)  20 m

e)   24 m