Simple .htaccess rewriting

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I am sorry if that question is a little silly. I am not so familiar with the .htaccess.

Assume that I have a file folder/index.php, it is dynamic. So, to access this, users need to enter something like folder/index.php?id=11111.

Now I want that the users can go to folder/index.php?id=11111 by entering only folder.php/11111.

How could it be done? Thank you very much if you can give a full solution.

RewriteCond %{QUERY_STRING} ^id=(.*)$
RewriteRule folder/index.php folder.php/%1?

that might work...