0 kg dog stands on a 18 kg flatboat at distance D = 6.1 m from the shore. It walks 2.1 m along the boat toward shore and then stops.

a 4.0 kg dog stands on a 18 kg flatboat at distance D = 6.1 m from the shore. It walks 2.1 m along the boat toward shore and then stops. Assuming no friction between the boat and the water, find how far the dog is then from the shore.