It looks like I'm doing this problem correctly, but my answer doesn't match the one given. It's negative, too - big no-no.
http://i111.photobucket.com/albums/n149 ... 1302894061
http://i111.photobucket.com/albums/n149 ... 1302894076
http://i111.photobucket.com/albums/n149 ... 1302894092
http://i111.photobucket.com/albums/n149 ... 1302894061
http://i111.photobucket.com/albums/n149 ... 1302894076
http://i111.photobucket.com/albums/n149 ... 1302894092