A runaway railroad car, with mass 30 x 10^4 kg, coasts across a level track at 1.5 m/s when it collides with a spring loaded bumper at the end of the track. If the spring constant of the bumper is 2 x 10^6 N/m, What is the maximum displacement of the spring after the collision? (assume collision is elastic) Please show work for first and best rating.