Please don't use unit rate to arrive at answer. I did that. It needs to be answered using unitizing. I already found the answer with unit rate. What I can't figure out is what is the difference between unitizing and unit rate. thanks
The comparison to find the value would be 12/5=x/9 because of comparing with ratios. The total cost divided by the amount gives the price per CD. If you leave it as a ratio you can find the missing variable since the increase in linear.
$12/5=$x/9. Multiply by 9.
$108/5=x. 9 Cd's will cost $21.6