Um. You need to know the speed of the piano to calculate the Newtons applied. Also, you can push something down an incline. You can push something down a declined though! Otherwise I'd solve this in a heartbeat.

If you neglect friction, the piano will accelerate down the ramp.  Without the man pushing, there is a force of gravity, wich is directed downward, and you divide this into perpindicular components, one of which is normal to the surface of the ramp.  The other force is the normal force of the ramp acting on the piano, which is equal and opposite to the component of the force of gravity that is directed normally into the ramp.  The net force is the component of gravity going down the ramp (I think it would be m*g*sin(10.4 degrees)).  If the piano is sliding at constant speed, there is NO NET FORCE acting on it, so the man's force on the piano must be equal and opposite to this force.  So, I think the answer is the man is pushing UP the ramp, with a force equal to 160*9.8*sin(10.4).

hmm...it -would- be dangerous to push a piano down a fictionless ramp,

Even if its only 10.4 :p