The worker lifted a 40 kg load to a height of 10 m using a movable block, applying an effort

The worker lifted a 40 kg load to a height of 10 m using a movable block, applying an effort of 250 N. Determine the useful force. If you can answer with a photo.

m = 40 kg.
g = 9.8 m / s ^ 2.
h = 10 m.
F = 250 N.
Apol -?
The useful work of Apol to lift a load to a certain height is determined by the formula: Apol = m * g * h, where m is the mass of the load, g is the acceleration of gravity, h is the height of the load.
Apol = 40 kg * 9.8 m / s ^ 2 * 10 m = 3920 J.
Answer: useful work when lifting the mobile unit Apol = 3920 J.