Solve Work Formula Problem: Calculate Force Exerted by Man

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Farm4Life
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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?
 
Where is the force due to the friction? The man's job is made easier by the help of friction.