Hi,
You can always view your current grade at
http://canasta.pftq.com/data/members/Wing_Hing_Leung/There is no limit on how many classes you can miss. However, the system grades you on attendance and you need an average of 80% by the end of the semester in order to pass. (I think it's 80%... check with William, he's the one setting the policy.)
If you are worried about not passing, you can always try to complete canasta decal's math problem sets for some extra credits. Here are the links to the problem sets:
http://canasta.pftq.com/gallery/albums/userpics/10024/ps1.pdfhttp://canasta.pftq.com/gallery/albums/userpics/10024/ps2.pdf