A man has plotted to blow up a building. The police have three suspects. They have received a letter telling the name of the suspect. But it is coded, to avoid one of the other members of the suspect's criminal gang realising what has happened and changing the letter. This is what the letter says:
2-1, 5-3, 3-2, 9-2
Which suspect is guilty: Alex, Dave or Jeff?
(Sorry about the storyline, I have real trouble coming up with them)