How to calculate the angle of a trajectory without knowing the velocity

Question

How do I calculate the angle of a trajectory to hit the target, without knowing the velocity. I only know the max height, offset height and the distance to the target.

This is what I got so far (I don't know how to calculate offset height ):

 float GetAngle(Vector3 startLocation, Vector3 endLocation, float maxHeight)
 {
         float distance = Mathf.Sqrt(Mathf.Pow(startLocation.x - endLocation.x,2) + Mathf.Pow(startLocation.z - endLocation.z,2));

         float offsetHeight = endLocation.y - startLocation.y;
         //how do I calculate offset height in this equation ?
         return -Mathf.Atan (4 * maxHeight/ distance ) + Mathf.PI;
 }

I use this to calculate the velocity (works fine I only need the correct angle):

float LaunchVelocity (Vector3 startLocation, Vector3 endLocation, float angle)
 {
         float range = Mathf.Sqrt(Mathf.Pow(startLocation.x - endLocation.x,2) + Mathf.Pow(startLocation.z - endLocation.z,2));
         float offsetHeight = endLocation.y - startLocation.y;
         float gravity = Physics.gravity.y;

         float velocity = range * range * gravity;
         velocity /= range * Mathf.Sin(2 * angle) + 2 * offsetHeight * Mathf.Pow(Mathf.Cos(angle),2);
         return Mathf.Sqrt(velocity);
 }

Answer 1

I got the solution:

float GetAngle(float height, Vector3 startLocation, Vector3 endLocation)
    {
        float range = Mathf.Sqrt(Mathf.Pow(startLocation.x - endLocation.x,2) + Mathf.Pow(startLocation.z - endLocation.z,2));
        float offsetHeight = endLocation.y - startLocation.y;
        float g = -Physics.gravity.y;

        float verticalSpeed = Mathf.Sqrt(2 * gravity * height);
        float travelTime = Mathf.Sqrt(2 * (height - offsetHeight) / g) + Mathf.Sqrt(2 * height / g);
        float horizontalSpeed = range / TravelTime;
        float velocity = Mathf.Sqrt(Mathf.Pow(verticalSpeed,2) +  Mathf.Pow(horizontalSpeed, 2));

        return -Mathf.Atan2(verticalSpeed / velocity, horizontalSpeed / velocity) + Mathf.PI;
    }