SIMPLE math-- Didn't I do this right?

[oooo]

In a physics experiment, students calculate the force of friction that a table exerts to stop a paper cone. When the ball starts at a height of 18 cm, the force of friction is 2.2 Newtons. What will be the force of friction if the ball starts from a height of 72 cm?

Wouldn't you set up a proportion and solve for x which is the force in Newtons? I did and got 8.8 N. Isn't that correct? For some reason, my homework is marked wrong and if I made a mistake, I want to know what it was.

(I also tried solving for their energies so that I could get work = the change in total energy so I could find the force using the work formula. I came up with 8.8 N with this approach also)

[Chi Meson]

I cannot picture this set-up. Where did the ball come from and how does it relate to the paper cone? How far did the cone travel?

Anyway, the force of friction is (ideally) independant of speed; if the cone remains a constant weight, and the table remains flat, then the force of friction will be the same no matter what happens.