draw shapes

1)  how do i draw shapes to the screen in silverlight  with vb.net? I used this but in vb.net but i dont know how to position the circle ?
        Dim bb As New Ellipse
        Dim aa As New Line
        Dim brush As New SolidColorBrush
        'Dim redpen As New Pen(Color.Red, 3)
        brush.Color = Colors.Black
     

        aa.X1 = 100
        aa.X2 = 300
        aa.Y1 = 10

        aa.Y2 = 50
        aa.Stroke = brush
        bb.Stroke = brush
        bb. ...