Determine the average power developed by a person when lifting a load for 1 minute 40 s to a height

Determine the average power developed by a person when lifting a load for 1 minute 40 s to a height of 15 m using a movable block, if he applies a force of 250 N. to the rope.

The average human power can be calculated using the formula:
P = A / t, where A is the work performed by a person, t is time (t = 1 min. 40 s = 100 s).
Useful work:
A = Pd * h, where Pd is the force acting on the load, h is the height to which the load was lifted (h = 15 m).
Since the movable block gives a 2-fold gain in strength, then Pd = 2F, where F is the force applied by a person when lifting a load (F = 250 N).
P = A / t = 2F * h / t = 2 * 250 * 15/100 = 75 W.
Check: W = N * m / s = W.
Answer: The average power is 75 W.