Silverlight - use combobox to select datagrid item - silverlight

Question

I'm a bit new to WPF and .NET, so this may be a simple task:
I have textblocks that get their values from the selected item of a datagrid. I'm trying to bind a combobox to one column in that datagrid so the user sees all the values in that datagrid column. When selecting an item in the combobox, it should make that row the selected item in the datagrid as well.
Here is my DataGrid:
<sdk:DataGrid AutoGenerateColumns="True" Name="l1dGrid" IsReadOnly="True" ItemsSource="{Binding}" DataContext="{Binding Path=DataContext}" />
and here is where the Datagrid gets data loaded:
_PCContext.Load(_PCContext.GetLine1_DownstairsQuery());
l1dGrid.ItemsSource = _PCContext.Line1_Downstairs;
Now I just need a combobox to have the ability to change the selected item in the DataGrid.Thanks in advance for any assistance!!!
[EDIT - SOLVED]
Ok, so I ended up just querying the datagrid based on the selected item of the combobox and setting the datagrid selected item to the one that matched that query.Here is the code I used to do this:
private void stockPick_comboBox_SelectionChanged(object sender, SelectionChangedEventArgs e)
{
string selection = stockPick_comboBox.SelectedValue.ToString().Replace("Line1_Downstairs : ", "");
selectGridItem(selection);
}
private void selectGridItem(string selection)
{
var stock = (from i in _PCContext.Line1_Downstairs
where i.Stock == selection
select i).FirstOrDefault();
l1dGrid.SelectedItem = stock;
}