expansion slots in a highway A. meet in the middle of the road to keep people from passing B. connect highways between states C. give a bridge room to expand and contract when the weather changes D. stretch the highway when there is not enough asphalt​

According to an observer on earth, planet x is stationary. maria and samir depart earth on their spaceships at the same time, each flying at 0.5c. maria flies toward planet x and samir flies in the opposite direction. according to maria, her voyage to planet x takes 9 years. how many years does maria's voyage take according to samir?