The D3100 doesn't have automatic bracketing, but it's easy enough to do it manually of course.
How do you do it manually ?
Ken Rockwell said:Exposure Bracketing: I never use this, and no one should. A holdover from the film days, I think it's finally been removed from the D40, hallelujah! Come on people, God gave you a big LCD: use it. Even in film days, Ansel thought bracketing was a crutch for the inept that usually ensures you get the wrong exposure on the one frame with the right gesture.