You must have energy to do work.
A person could not push the box and do work in the example above without a store of energy.
The person transfers 20 J of energy in doing 20 J of work pushing the box.
Work done = Energy transferred.
Calculate the work done by a crane when a mass of 200 kg is lifted 3 m vertically.
Upward force F = 2000 N
weight = mg
weight = 200 kg x 10 N/k
weight = 2000N.
Since the 200 kg object is being lifted vertically, the minimum upward force F equals the weight of the object.
Upward force F = 2000 N.
Work done W = Fd
F = 2000 N
d = 3 m
W = 2000 N x 3 m
W = 6000 J
The work done by the crane is 6000J.