Your question is not really about programming (the subject of this discussion
group), so this probably wasn't the best place to post.
Try working your way through this tutorial and it may help you understand
how to use Excel to do the sort of things you're asking about:
http://office.microsoft.com/training/training.aspx?AssetID=RC010233241033&pid=CR061831141033
The Excel functions you'll probably want to use are:
=NPER(<interest rate>,<payment>,<balance>)
That will give you the number of payments (months).
Note that the interest rate is per period (month), so will need to be the
annual rate/12.
=PV(<interest rate>,<number of payments>,<payment>)
Will return the total amount to be payed.
Do the NPER first so that you have the number of payments to enter.
Otherwise, nest the functions:
=PV(<interest rate>,NPER(<interest rate>,<payment>,<balance>),<payment>)
