How to set the selected value to Combobox in silverlight code behind

How to set the selected value to Combobox in silverlight code behind

How to set the selected value to Combobox in silverlight code behind.
Code as Follows :
<sdk:DataGridTemplateColumn Header="Risk">
<sdk:DataGridTemplateColumn.CellTemplate>
<DataTemplate>
<Grid>
<ComboBox Height="Auto"
x:Name="ComboRisk" Width="110"
ItemsSource="{Binding
Path=CusList,Mode=TwoWay}"
SelectedValuePath="{Binding Path=Risk,
Mode=OneWay}" SelectedItem="{Binding
Mode=OneWay, Path=Risk}">
<ComboBoxItem Content="High"
Background="#55A3FF"
IsEnabled="False" Margin="1,2,0,0"
/>
<ComboBoxItem Content="Test Time"
Margin="8,2,4,4" />
<ComboBoxItem Content="Yield Hit"
Margin="8,2,4,4" />
<ComboBoxItem Content="Quality
Impact (DPPM/Reli)"
Margin="8,2,4,4" />
<ComboBoxItem Content="Breaking
Download" Margin="8,2,4,4" />
<ComboBoxItem Content="ROM Update"
Margin="8,2,4,4" />
<ComboBoxItem Content="Low"
Background="#55A3FF"
Margin="1,2,0,0" IsEnabled="False"
/>
<ComboBoxItem Content="Good to go"
Margin="8,2,4,4" />
</ComboBox>
</Grid>
</DataTemplate>
</sdk:DataGridTemplateColumn.CellTemplate>
</sdk:DataGridTemplateColumn>
in the Code Behind I am doing like this :
ComboRisk.SelectedItem = bcomstask.Risk.ToString()