actionscript confusion

[SubFreeze Ver.2]

What does this mean?

_root.mc["hold"+i]._y = 128+113*i;

How does the 128+113*i work?

I am adjusting a script that was done for me, to make it so scrolling goes up and down instead of left to right (clients never make up their minds)

this.createEmptyMovieClip("mc",3);
mc._y =15;
mc._x =0;
for(i=0;i<7;i++){
mc.createEmptyMovieClip("hold"+i,i);
_root.mc["hold"+i]._y = 128+113*i; // This is the line I need to adjust by 10/15 pixels downward
_root.mc["hold"+i]._x = 15;
_root.mc["hold"+i].loadIt();
}

[jAQUAN]

128 and 113 might be the starting postition and height of the buttons. You should be able to adjust one of those + or - the 10/15 pixels you need.