I have been asked to solve this problem 2 ways. The first is unitizing and the second is unit rate. I solved it for unit rate. The problem states: A store is selling used CDs at five for $12. At the same rate how much will 9 CDs cost?
What is a unit rate? Thought it was used to describe price per pound or oz for food in a grocery store. Using unit rate I found $21.60 for 9 CDs. Thanks for help.

The unit rate in this case is $12/(5 CDs) = $2.40 per CD. The price for nine is then 9 CDs x $2.40/CD = $21.60, so your answer is correct.

Yes.. Your answer is correct