Useful Links:
http://standards.nctm.org/document/eexamples/chap6/6.2/index.htm
It will show you what the rate of change is.

http://www.investopedia.com/terms/r/rateofchange.asp
It will also tell you what the rate of change is.

http://www.teachertube.com/viewVideo.php?video_id=16499
This viedo shows you how to do a problem of rate of change.