(1) please post things in the correct folder.  you originally posted this in the folder for GMAT PREP problems; i have moved it to the correct forum.
(2) please 
ask a specific question.  read over your post again -- there's no specific question here.  your post basically just asks, "how do i solve assumption questions?"  that question, while obviously important, is much too general to answer in a forum post.
for starters, you may want to watch the march 4, 2010, video at the following link:
http://www.manhattangmat.com/thursdays-with-ron.cfm