Well, the answer is supposed to be 10 but I think there was probably a typo. :)
thanks so much for your help!
and yes, it was supposed to be 40.0 degrees. :)
For the question: A 435 n box is sliding down a 40.00 inclined. If the acceleration of the box is 0.250m/s2. Which formula would I use to find just the force of friction? and would I change the Newtons to kilograms?