What is the speed of the crate when it reaches the bottom?

Homework Statement

A 20.0-kg crate slides down an inclined plane that is 3.00-m high and 20.0-m long. If friction is negligible, what is the speed of the crate when it reaches the bottom of the plane?

W= F*D
K= 1/2 m*(v^2)

The Attempt at a Solution

They don't give me an angle so I'm not sure how I'm supposed to go about solving for the force parallel to the inclined plane. Once I have that I'll be able to finish out the problem. Help please!
(The answer turns out to be 7.67 m/s; I just need to know how to get there)

Just use conservation of energy. You have gravitational potential energy in the beginning. Don't bother with the work $$W=FD$$.