The network administrator has been asked to summarize the routes for a new OSPF area. The networks to be summarized are 172.16.8.0, 172.16.10.0, and 172.16.12.0 with subnet masks of 255.255.255.0 for each network. Which command should the administrator use to forward the summary route for area 15 into area 0?

Because all OSPF networks start with area 0, the new area would need to be anything but area 0, The correct option would be area 15 range 172.16.8.0 255.255.248.0 because this is the correct summarization of the networks in the new area 15. The summarization must come from area 15 to area 0, because all OSPF areas interconnect via area 0. The matching bits for the correct option, in binary, are:
172.16.8.0 10101100.00010000.00001 000.00000000
172.16.10.0 10101100.00010000.00001 010.00000000
172.16.12.0 10101100.00010000.00001 100.00000000