About the concept of work done (High school student)

Hi I am kind of Confused about an example in work done:

It says that a man applies 250 N parallel to the slope to push a box up a slope for 3 m, Now I know that the formula for work done if Force by Perpendicular distance which is 250 x 3 = 750 (which is the correct answer in my book). The thing is, isn't the object "Gaining" Gravitational potential energy ie change in its energy ie transfer of energy and therefor we should add that energy to the 750??
This is where I am confused.
Can any one help please :)


Edit: Or is the Force x Distance formula includes all changes in energy together?