What is the policy for questions that have been posted on multiple sites but only received a good answer on one?

Question

The question that sparked my interest was this one. The question was asked on money.SE and quant.SE, but only received a useful answer (according to the poster's comment on money.SE) on quant.SE.

Is there a policy for this? Based on my limited understanding of the SE system, I see several options:

1. Vote to close the question on money.SE and simply ignore it from there.
2. Flag the question for moderator attention and have it deleted from this site.
3. Copy the answer from quant.SE to an answer on money.SE. I would make my answer community wiki (I don't get reputation for it then, I think). I would copy the text of the answer from quant.SE verbatim, with a citation to the poster's comment and the quant.SE answer.
4. ???

For the sake of preventing link rot, I would prefer #3, even though option does somewhat duplicate content between sites. I think it makes it easier for someone stumbling across the question on money.SE to see the proper answer, without necessarily following the comment thread. Although this comment "thread" is only one comment long, I'm wondering about this in general.

Answer 1

Close it at least, but probably delete it.

There is already a link to the good answer. SE sites aren't in competition with each other, they are trying to make the Internet better.

I think with it closed (which isn't a bad thing) the content will fall off of our site and folks browsing won't be bothered by it. Because the questions are worded differently, I don't see an SEO penalty for either site. So if a search leads a user here, and they find the link to the good answer an Quant, then problem solved! The internet answered a question correctly for somebody.

But I would prefer to delete it altogether and save that user a click. That way a users who Googles with Bing will get a direct link to the answer they seek. You are very right about link rot, so removing the content that can go bad is better for us and for the Internet.