Alright, so you can kind of figure out what happens next. Hallway A is a bit misleading; it's a giant room that leads to the rooms where Big Boss would be. You'll be having your fights in that room.
They'll be heavily fortified, and are heavily, and uniquely armoured for you. So I'll leave it up to your creativity to start the fights. From now on, you may not write, in one post, that you eliminated all the targets. I will pose challenges for you. In other words, you will be writing for Cody's actual survival. The soldiers will be easy, if not annoying, but still dangerous. You may be able to get rid of them easy, but again, there will be challenges, and of course, Big Boss himself.
Do let me know if you have any queries, and notify me of anything you feel ought mentioning before posting!