The work done on lifting a box is equal to weight times the vertical distance it moves. (with a constant velocity)
W = Weight(Fgravity)*h
The weight of an object equals the mass(m) times the acceleration due to gravity(g).
W = mgh
But take note that there is also work done by gravity which is equal to mgh.
Wgravity = mgh
The net work done is equal to zero
W + (-Wgravity) = 0
