Detect x & y touch event in WP7 screen

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C#

I am really need help with return the coordinates x and y in the WP7 screen. this code help me to move an rectangle in the screen with showing the start(x&y), delta(x,y) and end(x,y) :

TransformGroup transformG;
        TranslateTransform translation;

        // Constructor
        public MainPage()
        {
            InitializeComponent();
            this.ManipulationDelta += new EventHandler<ManipulationDeltaEventArgs>(MainPage_ManipulationDelta);
            transformG = new TransformGroup();
            translation = new TranslateTransform();
            transformG.Children.Add(translation);
            rectangle.RenderTransform = transformG;
        }

        void MainPage_ManipulationDelta(object sender, ManipulationDeltaEventArgs e)
        {
            startX.Text =e.ManipulationOrigin.X.ToString();
            startY.Text = e.ManipulationOrigin.Y.ToString();
            DeltaX.Text = e.DeltaManipulation.Translation.X.ToString();
            DeltaY.Text = e.DeltaManipulation.Translation.Y.ToString();
            translation.X += e.DeltaManipulation.Translation.X;
            translation.Y += e.DeltaManipulation.Translation.Y;
            EndX.Text =Convert.ToString(translation.X);
            EndY.Text = Convert.ToString(translation.Y);
        }

I just want to do something like that but without move anything, just tap in the screen and know the start and the end with delta (difference). I use silverlight