Keiko walks once around a track at exactly the same constant speed every day. The sides of the track are straight, and the ends are semicircles. The track has width 6 meters, and it takes her 36 seconds longer to walk around the outside edge of the track than around the inside edge. What is Keiko’s speed in meters per second?
Answer Choices
A. \dfrac{\pi}{3}
B. \dfrac{2 \pi}{3}
C. \pi
D. \dfrac{4 \pi}{3}
E. \dfrac{5 \pi}{3}