I want to change the alpha value of sprite3 when the mouse roll over it

var sprite1:Sprite = new Sprite();
sprite1.graphics.lineStyle(2,0x000000);
sprite1.graphics.beginFill(0xCCCCCC);
sprite1.graphics.drawRect(0,0,200,200);
sprite1.x=50;
sprite1.y=50;
addChild(sprite1);
var sprite2:Sprite= new Sprite();
sprite2.graphics.lineStyle(2,0x00000);
sprite2.graphics.beginFill(0xCCCCCC);
sprite2.graphics.drawRect(0,0,200,200);
sprite2.x=300;
sprite2.y=50;
addChild(sprite2);
var sprite3:Sprite= new Sprite();
sprite3.graphics.lineStyle(2,0x00000);
sprite3.graphics.beginFill(0xfffff);
sprite3.graphics.drawCircle(0,20,20);
sprite3.x=150;
sprite3.y=125;
addChild(sprite3);
sprite1.addEventListener(MouseEvent.CLICK, clickSprite);
sprite2.addEventListener(MouseEvent.CLICK, clickSprite);
sprite1.buttonMode =true;
sprite2.buttonMode =true;
function clickSprite(event:MouseEvent)
{
sprite3.x=100;
sprite3.y=100;
event.currentTarget.addChild(sprite3);
}
var mouseLocText:TextField =new TextField();
addEventListener(Event.ENTER_FRAME, showMouseLoc);
function showMouseLoc(event:Event)
{
mouseLocText.text = “X=”+mouseX+“Y=”+mouseY;
mouseLocText.x =240;
mouseLocText.y =250;
mouseLocText.textColor = 6*14568752;
addChild(mouseLocText);
}
var mySprite:
mySprite.addEventListener(MouseEvent.ROLL_OVER, rolloverSprite);
function rolloverSprite(event:MouseEvent)
{
mySprite.alpha = 1;
}

this is my code i want to change the alpha value of sprite3 when the mouse roll over it. I dont know what variable type to put in( var mySprite:) so please help me friends