Solve Work Formula Problem: Calculate Force Exerted by Man

[Farm4Life]

I have pretty much figured out the problem, but i am unsure of my work.
the question reads:
a 330kg piano slides 3.6m down a 28degree incline and is kept from accelerating by a man who is pushing back on it parallel to the incline. The effective coefficient of kinetic friction is 0.40. Calculate: (a) the force exerted by the man.

F=mgsin(theta)
=(330kg)(9.81m/s2)sin90
F= 3237.3 N

Is this the correct formula to use to find the force exerted by the man?

 

[berkeman]

Where is the force due to the friction? The man's job is made easier by the help of friction.