Physics problem involving a penguin sled on a slope: Find the force required to stop it from sliding?

Here s the problem:

A loaded penguin sled weighing 80 N rests on a plane inclined at angle θ = 17° to the horizontal (see the figure). Between the sled and the plane, the coefficient of static friction is 0.27, and the coefficient of kinetic friction is 0.15. (a) What is the minimum magnitude of the force F , parallel to the plane, that will prevent the sled from slipping down the plane? (b) What is the minimum magnitude F that will start the sled moving up the plane? (c) What value of F is required to move the sled up the plane at constant velocity?

Here s the last answers I got:

a) 251N

b) 274N

c) 80.9N

But those are wrong. I ve tried this problem twice and I only have two attempts left. Can someone at least point me in the right direction on how to do it?