IP Addresses, subnets and more

Before I’ve always worked on smaller size Windows networks. I just started at a new location and a few things puzzle me. I don’t have access to the routers.

1. We have class B and Class C addresses assigned to workstations throughout the network (500+ pcs). These pcs are sitting next to each other and coming off the same switch. Example… One workstation could have an ip of 199.208.138.17, then pc next to it has an ip of 131.75.208.20.

What kind of routing do we have going on here ?
What should the subnet mask be for these workstations ?