Can I answer the closed question? if yes then how? because I am not able to answer it. Stack community is allow or not i am not sure about this point.
No, you can't answer a closed question. From the Help Center article "What does it mean if a question is "closed"?":
Closed questions cannot be answered, but can be edited to make them eligible for reopening.
You can try to edit the question so that it's a good fit for the community; if you do this within 5 days of the closure, the edit will push the question into the Reopen Votes review queue and other community members can decide whether to reopen the question or not.