1.She isn't old. She can't be in my class
 ----> she isn't old enough to be in my class
2.i am lucky.i have a lot of friends 
----> i am lucky enough to have a lot of friend
3. The bag isn't big. it can't carry everything
 -----> The bag isn't big enough to carry everything
4.Ba is not old.He can't drive his father's car
 -----> Ba is not old enough to drive his father's car
5.My English isn't good .I can't be a member of the club 
-----> My English is not good enough to be a member of the club