Okay, we have to separate the problem in two dimensions. X is going to be parallel to the surface of the plane, and Y is going to be perpendicular to X.(it's easier when you can see what I'm drawing). In X we have two forces, a fraction of the weight that pull the body down, and the friction, that goes against the movement (up). [Wx-Fric= m.a= 35.1,5]. [Friction= Normal force. Friction coefficient]. In the Y axis: Wy=Normal force. To find Wy and Wx we use a little bit of trigonometry, but it's easy. Wy=m.g. cos25° Wx= m.g. sin25° So, X would be: [m.g.sin25°]-[(m.g.cos25°).(friction coef)=35 .1,5 You just have to isolate the friction coef, and thats it.