selecting value in combo

Question

hi all,
this is my code:

<ComboBox x:Name="cmbImages" Margin="0,2,0,5"  > 
    <ComboBoxItem Tag="image/arrow_down_green.png"  >
    <StackPanel Orientation="Horizontal"> 
   <Image Source="image/arrow_down_green.png" Height="30"></Image>
</StackPanel>       </ComboBoxItem>     <ComboBoxItem Tag="image/arrow_left_green.png" >       <StackPanel Orientation="Horizontal">    <Image Source="image/arrow_left_green.png" Height="30"></Image>     </StackPanel>            </ComboBoxItem></ComboBox >

How can i select tag from code behind