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.

Question

I thought i have the right equation but my answer is not correct.

dog moves 2.3(3.5/21) m toward the shore

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

so 6.1 - .38 = 5.72 which is incorrect.

A little help please?