Halo 3 Spartan officer achievement?

[HaVoC]

I'm a lieutenant grade 2 and I have 89 Exp but I havent got the achievement, help.

 

[Andrew R]

Come on ask this in the game section little boy.

 

[Aero Ryder]

you can start by asking this in the gaming section, and not in the section where real people have been to war, which is not a game