A 4000-lb. automobile is supported on four springs each with stiffness k=150lb/in. When the vehicle is traveling over a caseway, a resonant verticle motion within it is excited. each span of the causway is 80ft in length and has a 0.75-in sag at midspan. Determine the maximum verticle displacement of the automobile when traveling at 65mph. Assume no damping in the vehicle.