Item 1: a link-only answer
Remove Page from being indexed in Google, Yahoo, Bing reads in its entirety:
I suggest you start here: http://www.robotstxt.org/
This is not an answer. The URL
http://www.robotstxt.org/ does not answer the question in any way, and the first part is wrapper text with no content.
There may be something on the site that the URL points to that answers the question. Given that the answer was accepted, there probably is. But the relevant content should have been included in the answer. As it is, this post is not an answer; it is at most a link to an answer. This is not appropriate on a questions and answers site. Stack Exchange is not Yahoo! Directory. (In fact this isn't even a link to an answer, it's a link to a site where there is a page or collection of pages that answers the question. The asker didn't even bother to point to the appropriate part of the site.)
Given that the site is relevant, and that the link is a hint towards the answer, it would have been appropriate to convert it to a comment.
Unfortunately, in practice, whether link-only answers are handled properly is hit and miss, it depends which moderator ends up handling your flag. I recommend downvoting and (optionally) commenting in addition to flagging; occasionally it results in the poster replacing their stub by an actual answer (but sometimes instead it results in revenge downvoting — people who post low-effort “answers” like this are often doing it for the rep and hate being criticized).
If you can (if you have the time and competence) and if it's useful (if the linked site is useful and there isn't already an answer that covers the information), please do post an answer based on the linked site.
Item 2: a code-only answer
Merge my 2 arrays in php reads in its entirety
This isn't a good answer, because it lacks an explanation. However, it does show comprehensible sample code, which is good. Since the question only asks how to make the code work and does not particularly call for a deep explanation, a code-only answer is ok.
(Some questions explicitly or implicitly ask why. On such questions, a post which only provides code without explaining why that code is correct doesn't answer the question and should be deleted.)
That code doesn't correctly answer the question. This is a reason to downvote, not to delete.
This is on the border between a deletion-worthy very-low-quality answer and a non-deletion-worthy rather-low-quality answer.
Converting to a comment would not be appropriate. Conversion to a comment is appropriate for a useful remark that doesn't answer the question but provides an insight or hint. This one doesn't.