physics help
posted by mike .
a 3.5 kg dog stands on a 21 kg flatboat at distance D = 6.1 m from the shore. It walks 2.3 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.
I thought i have the right equation but my answer is not correct.

wouldn't the dog move 2.3(3.5/21) m toward the shore?

then you would subtract the overall distance and the answer above? right?

remember that the boat moves as well...the dog is a system and the boat is a system