A spring is mounted horizontally with its left end fixed. By connecting a spring balance to the free end and pulling to the right, we determine that the stretching force is proportional to the displacement and that a force of 6.0 N causes a displacement of 0.030 m. We remove the balance and connect a 0.50 kg slider to the end, pull it until it moves to x = 0.020 m through a frictionless air track, release it and see how it oscillates. Determine the slider position after 3.5 seconds.