Tweenclass question

so im using tweenclass for an image. It’s like this…the image has 4 points on it that i need to center on the stage whenever you rollover its corresponding button. I want it to go from spot to spot, NOT from an origin. Here is what im using for the rollovers…

import mx.transitions.Tween;
import mx.transitions.easing.*;
stop();
this.btn_1.onRollOver = function () {
btn_1._parent.gotoAndPlay(“OVER”);
var myTween:Tween = new Tween(_root.pic,"_x",Strong.easeInOut, _x, -100, 2, true);
var myTween:Tween = new Tween(_root.pic,"_y",Strong.easeInOut, _y, -100, 2, true);
}

obviously the _x after the ease is whats wrong. It starts from the same point all the time and i want it to start from whatever point its on…make sense?