Do I detect a faint scent of homework here? That would be off topic for this board.
Can be a problem if the routers that advertise that route to the backbone area (area0) is always the same ospf area ? In this case area and the router should be a stub area
Quick answer: Probably less so because of R11,R12,R13 belonging to the same area, but there might still be some issues, depending on how you generate the route on R11,R12,R13 (internal route vs external route; there's special rules in OSPF w/regards to stub areas and what goes into them or comes out of them) and possibly how the ABR is set up for summarization.
In this thread at learningnetwork.cisco.com
https://learningnetwork.cisco.com/s/question/0D53i00000Kt0WaCAJ/stub-area-receiving-normal-routesnetworks , we can find this wonderful illustration by user "amascuba", the best I have found yet (although there's a typo in "ABSR" which should be "ASBR").
That should get you started to find the answers.