Answer:
Revolution traveled by me = 30π ft.
Revolution traveled by my friend = 20π ft.
Difference between revolutions = 10π ft.
Explanation:
In one revolution, I travel 2π(15) = 30π ft., and my friend travels 2π(10) = 20π ft., so my revolution is 30π - 20π, or 10π, ft. longer than my friend's revolution.