Zoom In/Out - How to get the number right?

programming flash
1

I am having a little trouble zooming in an out… How do I get the zoom to zoom in and out on the exact position on the middle of the game screen?


        function zoomOutFunction(e:MouseEvent):void {
            Game.levelHolder.scaleX = .60;
            Game.levelHolder.x += midX/2.5;// Something I tried to add: - (Game.levelHolder.x / 2);
            Game.levelHolder.scaleY = .60;
            Game.levelHolder.y += midY/2.5;// Something I tried to add: - (Game.levelHolder.y / 2);
        }
        function zoomInFunction(e:MouseEvent):void {
            Game.levelHolder.scaleX = 1;
            Game.levelHolder.x -= midX/2.5;// Something I tried to add: + (Game.levelHolder.x);
            Game.levelHolder.scaleY = 1;
            Game.levelHolder.y -= midY/2.5;// Something I tried to add: + (Game.levelHolder.y);
        }