Amtrak plans to extend their railroad network to a big islan

Amtrak plans to extend their railroad network to a big island, which is connected to the continent by a bridge. According to the plans, there will be M stations on the island. There are two types of stations: the first type are hubs that connect 4 railroads, the second type are dead-end (terminal) stations, with only one railway line. To reduce the costs, the railroads don\'t make loops, that is, there are no simple cycles in the network, so the system is cheaper, although all stations are connected. Only one of the hubs is directly connected to the outside world. How many hubs, and how many terminals will be built? (The total number of stations is M).

Solution

M=9stations..

Hubs=4 stations

Terminals=5 stations