Finding the coefficient of friction on a 25-degree ramp

[ben811]

A box that weighs 500N is sliding down a ramp at a constant speet. The angle the ramp makes with the horizontal is 25 degrees. What is the coefficient of friction between the box and the ramp?

Can anyone give me some direction in how to approach solving this? I understand that
Ff=u*Fn, but I can't figure out how to find Ff.

 

[arildno]

Well, what is the NET force acting upon the box, in both the normal&tangential directions?