Problem A does deal with rotational motion, but this problem involves the conservation of angular momentum. But then after reading it I realized different principles were involved. The example question deals with Newton's second law, while Problem a deals with a collision, thus both energy and momentum. Problem b deals with Newtons second law, like the example question but instead of looking for force, it is asking for mass. I chose B because A has a clear before and after that is not so in the original problem.
B seems more similar because it is evaluating force.
That is both problems examine the force between objects. Other question b involved an angle, which brings vectors into play.