I don't know how to solve this problem. In it, I am given the mass (4 kg), acceleration (0), velocity (20 m/s), coefficient of friction (.2), and the applied force (10 N downwards with an angle of 30 degrees above the horizontal). I must find the displacement of the object if the force is removed.

the object is moving at 20 m/s

when the force is removed, the object will be decelerated to a stop (over some distance) by friction

find the frictional force (m * g * .2)

find the deceleration
... a = f / m

find the stopping time
... t = v / a = 20 / a

find the stopping distance
... d = [(20 + 0) / 2] * t