In the notes I have also assigned IP addresses 172.16.5.1 to Workstation A and 172.16.5.2 to Workstation B.

Even though these two workstations are physically connected to same switch or hub and the physical network may be single network but the logical network is a completely separate issue.

On one logical network we have 172.16.5 as our network, and the other logical network is 192.168.0.

We have a logical network and physical network and it is important to distinguish between the two, even though share the same physical hub, they logically are on completely separate networks

These two machines, or these two logical networks would be incapable of talking to one another and we would need to put a router between them in order to get them to talk to one another.