David is painting a wall and needs to reach a point 3.0 meters high. David's height is 1.8 meters, and he can extend his arm 50 centimeters above his head. He uses a ladder to reach the required height. The top rung of the ladder he stands on must allow him to just reach the 3.0-meter mark. What is the height of the ladder's top rung from the floor, in centimeters?