The most difficult chapter yet... number 9

Well the most difficult part about this chapter is getting the formulas correct. I spent at least 2 1/2 hours on the homework because after i finished all of the work, I would go back and my answer was incorrect. It took me forever to find out what I did wrong. The formulas are lenghty, but I understand their applications. I don't think there is anything too difficult to understand, it is just simply knowing which formula and putting the numbers in correctly.