As Andrew C says, it could be the first usable address on the subnet; sometimes it's the last usable. On a lot of networks (not always/not a rule) you can figure this out looking for the 'nearest' L3 address: a router interface or L3 switch SVI that the device can get to (this can be behind different L2 devices).
Can you post the topology here? Or describe it in a bit more detail?
Simply take the 100th address as a default gateway e.g. Fa0/0 188.8.131.52 its very simple, you just have to give an IP address to the interface connecting with your router giving you access to other networks, its your gate to enter and exit from your network and that gate has some IP could be any IP first or last usable address of your subnet. Hopefully this help.
Keep it simple.
"Back in the day" routers were often called gateways (routers separate broadcast domains). The DG is how users on the LAN get out of the local subnet into the wild blue yonder.
The DG can be acquired from the DHCP server (typical) or you can manually configure it per device.
If a PC is sending a packet but doesn't know where the destination is it just sends it to the router (DG), and he will deal with it.
Routers have a somewhat similar concept, but its called the default route, or Gateway of last resort...which is necessary if you want to send packets to a destination but you don't have a route in the routing table for it...if you do have a GOLR, then the router just sends it to the next router and maybe he will have a route for it.
Gateway of last resort is not set
184.108.40.206/32 is subnetted, 1 subnets
C 220.127.116.11/32 is directly connected, Loopback5
18.104.22.168/32 is subnetted, 1 subnets
C 22.214.171.124/32 is directly connected, Loopback7
126.96.36.199/32 is subnetted, 1 subnets
C 188.8.131.52/32 is directly connected, Loopback9
10.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
C 10.1.1.0/30 is directly connected, GigabitEthernet0/0
L 10.1.1.1/32 is directly connected, GigabitEthernet0/0