Determining sequence of oligoribonucleotide
Here are a few hints which might help you:-  

1) You get free UMP and CMP (in contrast to UMP + C or CMP + U) in the second experiment before alkaline hydrolysis.  

2) There are two CMP in "N" oligoribonucleotide, and a free cytidine (and not CMP) in "M" and "Q". 

3)Use the fact that all oligoribonucleotides were treated with phosphatase before being subjected to alkaline hydrolysis.   

(Referring to your comment, I dont know why do you think consecutive cytidine is not possible).

These are a few hints that helped me solve this. If you want further clarification or the answer, tell me in the comments.  

Answer for reverse derivation:- $5'-UACGCCGAC-3'$