Based on the wording of this problem, you're going to have to make an assumption or two. One is the highly problematic value of g = 10 m/s^2. (9.8 is much closer to the actual value). The other is that the mu given is the coefficient ofstaticfriction.

So, if you think about the runner pushing backwards against the track, how would you draw a free-body diagram? How is friction modeled?