As one of the most harmful natural disasters to mankind, post-earthquake rescue is a huge rescue project, including personnel search and rescue, medical rescue, disaster relief materials supply and many other aspects, which has long been concerned, among which the post-earthquake disaster relief materials supply is one of the focuses of people's attention.

Usually, helicopters and trucks are the main tools for the supply of disaster relief materials after the earthquake. For drugs, medical devices, food, water and other urgently needed materials with high timeliness requirements, air transport is generally used. Of course, when the road is damaged and ground transportation is impossible, air transportation is also needed. However, due to the limited number of helicopters and the high transportation cost, ordinary materials in the rescue points that have been repaired after the roads are not damaged or damaged are mainly transported by trucks.

Immediately after an earthquake occurred in a certain area, a post-earthquake rescue command center was established. The command center obtained the state information of various rescue points in this area after the earthquake through satellite, aviation and other remote sensing image data and some actual feedback information (see annex 1). See annex 2 for the information of transportation provided by the command center at present. If each person who needs rescue needs 1 kg of urgently needed materials and 5 kg of ordinary materials every day, and the command center can equip each emergency distribution center with sufficient transportation. Please solve the following problems through modeling and analysis:

1. In order to facilitate the transportation of relief materials, the command center decided to set up four emergency distribution centers in the earthquake zone. Suppose that when the road is fully restored, the number of people who need to be rescued at each rescue point is a quarter of the population of the rescue point. Please choose the best location for the four emergency distribution centers to be built by the command center, so as to minimize the transportation cost when the roads at all rescue points are completely restored.

2. If the epicenter is located at 19 km east of the command center, if the number of people who need rescue decreases with the increase of the distance from the rescue point to the epicenter, there is a relationship: the symbol ""is rounded up and the symbol ""is rounded down. Under the condition that the question 1 other conditions remain unchanged, please re-select the best locations of the four emergency distribution centers for the command center.

3. According to the location of the four emergency distribution centers determined in question 2, the concrete plan of material transportation on the second day after the earthquake is given (that is, how many times each emergency distribution center needs to send helicopters and trucks, and the route that passes through the rescue point each time), and the transportation cost of that day is calculated.

4. In practice, with the passage of time after the earthquake, the self-rescue ability of rescue points will be continuously enhanced, the damaged infrastructure will be continuously restored, and the number of people who need rescue will be continuously reduced. Suppose there is a relationship from the second day after the earthquake:

On the basis of question 2, please determine which rescue points will need less than 100 people on 16 days after the earthquake; If the number of people who need rescue at the rescue point is less than 100, the command center will no longer carry out rescue, and those who need rescue will be rescued by their own rescue points. Please determine how many days after the earthquake, the transportation cost will be half less than that of 1 that day.

Note: 1) The coordinates of all rescue points are calibrated relative to the command center;

2) The straight-line distance of helicopter transporting materials, while the distance of truck transporting materials is the sum of the absolute values of the difference between abscissa and ordinate;