An 81 kg boat that is 9 m in length is initially 7.8 m from the pier. A 20 kg child stands at the end of the boat closest to the pier. The child then notices a turtle on a rock at the far end of the boat and proceeds to walk to the far end of the boat to observe the turtle. How far is the child from the pier when she reaches the far end of the boat? Assume there is no friction between boat and water.