Whats Legal But Not Logical, Logical But Not Legal

A Boy Failed In exam. He Said 2 His Teacher: I'll ask U a Question. If u dnt 
answer u'll hve 2 give me A Grade"
Teacher: OK
Student: Whats Legal But Not Logical, Logical But Not Legal & Neither
Logical Nor Legal? 
Teacher Cudnt Answer.He Gave Him A Grade Later the Studnt Answered:
Sir, U R 63 Yrs Old & Ur Wife Is 30. Thats Legal But Not Logical.
Ur Wife Has a 25 Yrs Old Boyfriend, Its Logical But Not Legal.
Now U Hav Given Ur Wive's Lover A Grade. Thats Neither Logical Nor Legal...