Moving a mask

Hey all,

I’m using masking moved by actionscript to accomplish a panning effect on an automatic slideshow. How, if I’m using this script:
[AS]onClipEvent (enterFrame) {
choice = Math.round(Math.random()*0);
switch (choice) {
case 0 :
this._x = _x + 25;
if (this._x>= 360){
this._x = -360;
do I get it to move across the stage (from -360 to 360) in a certain amount of time? The photos are changing at a speed of 25 (I’m guessing that means frames, I’m a newbie when it comes to action script), so I’d like the mask to move at the same rate.

Thanks in advance, you guys are great :nerd:

PS - there will be other cases, as soon as I figure this one out :wink: