The graphs show the force Fi (in pounds) required to move an object 9 feet along the x-axis. Order the force functions from the one that yields the least work to the one that yields the most work without doing any calculations. Explain your reasoning.

http://img227.imageshack.us/img227/9098/picrn.png

Give me some hints, please? I don't know anything about physics, but I think this is from a physics section of problems in my textbook.

EDIT: I made a booboo with the title, sorry.