The boxes push downward with a force of 1000 N: this means the total weight of the boxes is 1000 N, and then the forklift must do an equal (and opposite) force in order to lift them.
The 5 boxes are lifted by an altitude of [tex]d=2 m[/tex], so the work done by the forklift is equal to the product between the magnitude of the force done by the forklift times the distance covered by the boxes:
[tex]W=Fd=(1000 N)(2 m)=2000 J[/tex]
