This article will also explain an articles expiration date and how it can be extended.

Questions have a 4-day open period. If your question doesn’t receive any answers within this time frame, it will expire and be deleted. However, before the question expires, you have the option to extend the time period a question is open. You can extend it one time (and only once) by 4 more days to a total of 8 days.

To extend the open period for your question, go to the question and click Edit (pencil icon) in the action bar below the question, then select Extend Expiration from the option menu.

If nobody answers your question after 8 days and your question expires, you can try rewording your question and asking it again or search Yahoo! Answers to see if anyone else has received an answer to a similar question.