check out
http://www.bobtait.com.au/
If your not the most proficient at theory try bobs books , I did 2 CPL subjects in his classes and self studied the rest using his books, had no issues , hes a real character !
heres a extract from his CPL Performance book
-What if the ZFW is not in the envelope ?
1.You may shift your weight
2.You may add extra weight as ballast
3. you may subtract weight and leave it behind
4.You may do any combination of these
5.You may slash your wrists
ha good luck next time !