Answer: The riders are subjected to 11.5 revolutions per minute
Explanation: Please see the attachments below
The body will take 20 seconds to cover a distance of 1000 m i.e. 1 km
Actual Mechanical Advantage(AMA) = Weight / Force
Here, Weight = 764 N
Force = 255 N
Substitute the values in to the expression,
AMA = 764 / 255
AMA = 2.99
After rounding-off to the nearest tenth value, it would be 3
Finally, option C would be your answer.
Hope this helps!