Once you have the Guru achievement, you only need the level 6 answers to get this achievement. So first of all, make sure you have unlocked
and then here are all the answers for level 6, in order of how many characters are in the answer.
Wreck It Ralph
The Book of Life
The Hunger Games
Also note that many people report this achievement as being buggy. If it does not unlock, you may need to reinstall the game and complete it again.