Assuming there's no friction, we have a net vertical force acting on the crate of
∑ F[vertical] = n - W + f sin(-20°) = 0
where n = magnitude of normal force and f = magnitude of applied force. It follows that
n - W - f sin(20°) = 0
n = W + f sin(20°)
and there's not much more to say without any additional information.
