Help with alpha fade!

1

I have a button that effects the alpha of an MC on mouseover. I can’t figure out how to create a fade with the alpha shift.

This is what I’m using right now. AS is placed on button that controls the MC.

on (rollOver){
_root.background.frame_2._alpha = 25;
_root.background.frame_3._alpha = 25;
_root.background.frame_4._alpha = 25;
_root.background.frame_5._alpha = 25;
_root.background.frame_6._alpha = 25;
}
on (rollOut){
_root.background.frame_2._alpha = 100;
_root.background.frame_3._alpha = 100;
_root.background.frame_4._alpha = 100;
_root.background.frame_5._alpha = 100;
_root.background.frame_6._alpha = 100;
}

Thanks for any assistance.