Configure the serial backhaul.
Configure routing for the backhaul. This is a failover for your network so it is only used if the border interface is down.
Configure a static route with a higher administrative distance to 0.0.0.0 which will make a failover. The lab problem is to figure out how to do this.
For documentation. Disconnect your fast 0/0 interface and see if your packets route out to the 10.0.0.1 (can you ping 10.0.0.1).
Note: On this network 172.16.13.100 is my router.
This is a special bonus lab. Doing it will definitely get you some extra points in the class.