As always, if you find while working these problems that you need further practice, I would suggest trying some of the other odd-numbered problems (answers to odd exercises are in the back of the book) or asking the TAs or myself questions in office hours.
Chp 11
11-8 (p. 369)
Chp 12
12-15 (p. 392); 12-16 (p. 393); 12-18 a-f (p. 393) (do as many parts as you need to before you feel that you've got it)