When surveying a sea island, a surveyor erects two vertical poles 1,000 pu apart. The poles are 5 pu tall, and the poles and the island lie in a straight line. When the surveyor walks 123 pu back from the front pole and looks up at the peak of the island from ground level, the tip of the pole lines up with the peak. Similarly, when the surveyor walks 127 pu back from the rear pole, the tip of the back pole and the peak of the island line up when observed from ground level. Liu Hui asks the reader to find the height of the island and the distance from the island to the front pole