Each floor has a cable length requirement up to 150 meters. Each branch is 20 miles away from main office. Your job is to link the main office and 3 branches together. LAN or LANs can talk to the main office. Must be inexpensive.
Installation is easy.
On each floor use an active hub with UTP cable. A diagram shows a 10Base2 segment with 2 terminators both grounded. Hanging off the thinnet are six 8-ports UTP hubs with PCs and 1 server. Each hub has a BNC port connecting back to the thinnet. PC users are intermittently unable to talk to the server.