Answer
a. 5400 m.
b. 4500 s, or about 75 minutes.
Work Step by Step
a. Using the hint, find the area between the concentric circles, and set it equal to the length multiplied by width of the path. Let R1 and R2 be the small and large radii.
$$\pi R2^{2} - \pi R1^{2} = lw$$
$$l = \frac{\pi R2^{2} - \pi R1^{2}}{w} = 5.4 \times 10^{3} m$$
b. $t = \frac{l}{1.2 m/s} = 4500 s$.
