Try this worksheet!

https://docs.google.com/a/nssd112.org/document/d/1S8AsccDISa6U4hpK_z6UHdMTn8eBmhPbuKCCR_3tImM/edit?hl=en_US&authkey=CJmB0pgG&pli=1

If you'd like, print it out and give it a shot.  Email me with questions or comments.