Assistance with Homework

[CoconutMikeNIke]

I know that the majority of people here are in school, whether it be high school, college, or still somewhere below that.  Schools, for the most part, always give homework.  And the problem arises, what if you don't understand all of the homework given to you?  You could look online for a quick lesson in the subject, or call a friend, but pages online aren't the most personal and can sometimes be just as hard to understand.  You could call your friend, but let's say that your friend isn't taking the same course, or is as clueless as you.  What's a person to do?  That's what the idea of this thread is for.  I want people to come here and ask their questions, with advice from people who may be able to help.  It can be any subject, from coming up with a thesis for a US History paper, to trying to understand a reaction at equilibrium for a chem test, and any grade as well.  Basically, You set up the question by stating the subject/class/course/etc., to keep confusion to a minimum, and ask in as much detail as seems needed, ask the question.  I won't say that this is going to be the most riveting of conversation pieces, but I hope it becomes helpful.  Also, it would be advised to ask as soon as possible when you need help, so that a suitable answer can be found before the day it is due.

Now, the reasoning behind this isn't completely altruistic, as I'm actually looking for some help.  This is for AP Calculus.    Related rates.  I missed a class last week, and don't fully understand how to set up the problems.  Right out of the book, the question asks

A spherical balloon is to be deflated so that it's radius decreases at a constant rate of 15 cm/min.  At what rate must air be removed when the radius is 9 cm?

Now the book I'm using gives answers for odd numbered problems, and the answer for this one is 4860pi cm³/min, and I don't understand what to do to get that.  Saying that it's a spherical balloon, I imagine it might have something to do with the volume formula, but I honestly don't know, I only did two practice problems on Thursday during class.  Essentially, what I am asking is, what information do I use, and could someone give me just a hint as to what I should do with the info?  Here's hoping this was a good idea...

[MEGAߥTE]

So radius is obviously one of the variables, r.
A rate is a derivative with respect to time, so you have dr/dt for the change in radius and dV/dt for the change in volume of air that is being removed.
Now you need an equation to solve.
They tell you that's it's a spherical balloon, so you can use the equation of a sphere: V=4/3*π*r³
Use that equation to relate the rates.
Is that enough, or do you need more help?

[CoconutMikeNIke]

Oh, okay, thanks.  That should be enough.  For future reference, though, what do I hit to make the pi symbol?

[MEGAߥTE]

There isn't a button; you can go into Character Map if you use Windows.

[ShadowBrain]

Best thread of the year, right here. Of course, I'll have to explain why I'm on the FF when I'm supposed to be doing homework....