How do I fix this?I notice it when I pressed post question but then a red box appeared, the questions stay the same but the tags were changed.
The exact tags on a closed question don't really matter. Usually, if a question is about physics and is on-topic here, then the question is probably about acoustics, since other areas of physics are almost always off-topic here.
If you want to ask questions about physics in any area, there's a separate web site for that: https://physics.stackexchange.com/.
One note: The question you posted here that asks for help solving two problems probably won't be answered at the Physics stack linked above, since neither this site nor that one will help you solve homework problems, and it appears you are asking for homework help.