Sometimes, an answer for a question A also works for a question B. While question A & B are different questions and are not really duplicates (as questions), but the answer is an answer for both. Should we just add a related comment or should we close as duplicate?
Questions should be closed if they are duplicates and not if the answer happens to be the same. There is also an official policy for this, but I can find it right now. However, I could find Joel Spolsky's answer to a similar question.
Somebody should vote to close; that will give the user the big banner. On SO, it's common as dirt for the question to be all wrong. They think the issue is "null reference exception" but it's really "product is looking in the wrong folder". So I will not hesitate to mark as dupe if the answers to A take care of B also.
Here, you might think a person knows if they want "how to get to the airport from XYZ" but you know, if the answers to "how to get from XYZ to the airport" work, then they work, right? So I won't mind if after that first vote-to-close, 4 more happen to come along. But you don't need to worry about 5 votes, only about your own.