Aman is walking while riding a train. he says he is moving at 2 mph. a woman standing on a platform at a train station says the man on the train is moving at 72 mph. which person is correct?

The man of mass m1 and the woman of mass m2 are standing on opposite ends of the platform of mass m0 which moves with negligible friction and is initially at rest with s = 0. the man and woman begin to approach each other. derive an expression for the displacement s of the platform when the two meet in terms of the displacement x1 of the man relative to the platform.