To resolve the IP conflict and achieve the desired setup, you can configure the WAN1 interface with the IP address 200.200.20.2 and the subnet mask 255.255.255.248, along with a gateway of 200.200.20.1 for department A. Then, configure the WAN2 interface with a secondary IP address of 200.200.20.3 and the same subnet mask. This allows you to assign both IP addresses to separate departments. To ensure outgoing traffic from department B uses the correct IP, set up an IP pool or source-based routing to route traffic from department B through the WAN2 interface with the source IP of 200.200.20.3.