Can people please reopen this question.
Or can they give me a reason as to why it is an off-topic question?
I'm one of the people who voted to close. There are several ways this question took a wrong turn, and I'll try to explain them to you.
First, one thing that annoys a lot of people to death is that you didn't show your work. You didn't show how you got your answer, you didn't show any work that the book did to get its answer, you just gave the problem, your answer, and the book's answer, and was like "figure it out for me!" and people get really annoyed by that kind of attitude. Why? The people on this site are volunteering their time to answer your questions. Most of these people are professors, physicists, and in short, very smart people . You're asking these incredibly smart people who are volunteering their time here to do something as mundane as your homework; the least you can do is make it a little easier for them to figure out the problem by showing your work. If you show your work, people will respect you a lot more here.
Second, the problem is a homework problem. Homework is used in a bit looser of a way on this site. Basically, any problem that is some kind of arbitrary type exercise is a homework problem, and we don't exactly appreciate those here. What we simply ask, to prevent questions that just spill the problem onto the page and ask people to solve it, is that you ask a conceptual question - in other words, ask about the thought process, not the actual solving of the problem. You can give the problem to help explain the context, but in the end, we want the answer to your question to be applicable to other people's questions as well, so try to keep that in mind. If your question isn't generalized enough, that is, it really is just, solve this problem, it's probably going to get closed.
It is also a check my work question, which we just don't allow here. We find they aren't productive questions and don't help anyone else on the site. One thing to keep in mind is the purpose of this site isn't just to help you, it's to help everyone else who has questions about physics. A check my work type question only helps you, and while that is part of the purpose of this site, that isn't the full purpose.
For these reasons, the question was closed, and will not be reopened. However, if you have a conceptual question, then please ask that, as a separate question, and if it follows the rules of the site, it will be answered. I hope this helps!
 I am not one of those people, I am in fact a middle school student, and I'm very grateful to everyone on this site who takes their time to answer my often-dumb questions. In a nutshell, I don't want you to take this as a criticism of you - this is a mistake a lot of people make when trying to ask questions on this site.