Spreading duplicated mc's

hi, i am trying to create a list of buttons populated from an xml file

they populate but i DONT want them to align with x starting at 0

this is what i got

gridX = 30;

for(var i=0; i<proAmmount; i++) {
proBtn.duplicateMovieClip(“proBtn”+i,i);
_root[“proBtn”+i]._y = gridX*i
}

i want to be able to start the first buttons _x at lets say 100 or something and then space them out 30 px apart…

please let me know if you can help thanks