Question 1:  5 marks

Question 2a:  5 marks:
3 for the grammar
2 for the explanation

Question 2b:  5 marks (same as 2a)

Question 3:  7 marks
3 marks for informal description
4 marks for formal PDA.  You can mark either the diagram or the table,
  whichever you think is easier to do.  You don't have to mark both
  (or check that they are equal).

Question 4a:  3 marks.  
I don't expect the same level of formality as in the solutions.  If
the argument is written more at the level of the intuition paragraph I
give, that's okay, as long as it has all the crucial elements (the
function starts out positive, it goes negative at some point, it can't
jump from positive to negative without hitting 0).

Question 4b:  4 marks.  

Question 4c:  4 marks.

Question 5:  5 marks.
1 mark for the right answer (not context-free).
4 marks for the proof. 

Total:  38 marks.