A group of people with total mass 1500 kg stands in a boat with mass 12,000 kg at rest in frictionless water. If the whole group walks 6.5 m from bow to stern, how much does the boat move in meters. Assume x=0 corresponds to the initial location of the center of the boat (i.e. the bow is at -3.25m and the stern is at 3.25m).