Silverlight / WPF - Computed Columns In WPF DataGrid

hie,
   I want to created computed columns like ms excel in wpf customized datagrid.Can anyone suggest some idea.for eg i have datagrid in following format:

 <DataGrid Name="dgv" Grid.Row="1" AutoGenerateColumns="False">
        <DataGrid.Columns>
          <DataGridTemplateColumn>
 <DataGridTemplateColumn.CellTemplate>
              <DataTemplate>
                <Grid Name="grdCell">
                  <Grid.RowDefinitions>
                    <RowDefinition Height="*"></RowDefinition>
                  </Grid.RowDefinitions>
                  <Grid.ColumnDefinitions>
                    <ColumnDefinition Width="0"></ColumnDefinition>
                    <ColumnDefinition Width="50"></ColumnDefinition>
                    <ColumnDefinition Width="50"></ColumnDefinition>
                    <ColumnDefinition Width="50"></ColumnDefinition>
                    <ColumnDefinition Width="50"></ColumnDefinition>
                    <ColumnDefinition Width="50"></ColumnDefinition>
                    <ColumnDefinition Width="50"></ColumnDefinition>
                    <ColumnDefinition Width="100"></ColumnDefinition>
                    <ColumnDefinition Width="50"></ColumnDefinition>
                  </Grid.ColumnDefinitions>
                  <!--<TextBox Name="tempTotal" Grid.Row="0" Grid.Column="0" IsReadOnly="True" Focusable="False" Visibility="Collapsed">
                    <TextBox.Text>
                      <Binding Path="tempTotal" UpdateSourceTrigger="PropertyChanged" Mode="TwoWay"></Binding>
                    </TextBox.Text>
                  </TextBox>-->
                  <TextBox Name="txtDays" Grid.Row="0" Grid.Column="1" IsReadOnly="True" Focusable="False">
                    <TextBox.Text>
                      <Binding Path="days" UpdateSourceTrigger="PropertyChanged" Mode="TwoWay" ></Binding>
                    </TextBox.Text>
                  </TextBox>
                  <TextBox Name="txttank1" Grid.Row="0" Grid.Column="2" Background="Yellow">
                    <TextBox.Text>
                      <Binding Path="tank1" UpdateSourceTrigger="PropertyChanged" Mode="TwoWay" ></Binding>
                    </TextBox.Text>
                  </TextBox>
                  <TextBox Name="txttank2" Grid.Row="0" Grid.Column="3" Background="Yellow">
                    <TextBox.Text>
                      <Binding Path="tank2" UpdateSourceTrigger="PropertyChanged" Mode="TwoWay" ></Binding>
                    </TextBox.Text>
                  </TextBox>
                  <TextBox Name="txttank3" Grid.Row="0" Grid.Column="4" Background="Yellow">
                    <TextBox.Text>
                      <Binding Path="tank3" UpdateSourceTrigger="PropertyChanged" Mode="TwoWay" ></Binding>
                    </TextBox.Text>
                  </TextBox>
                  <TextBox Name="txttank4" Grid.Row="0" Grid.Column="5" Background="Yellow">
                    <TextBox.Text>
                      <Binding Path="tank4" UpdateSourceTrigger="PropertyChanged" Mode="TwoWay" ></Binding>
                    </TextBox.Text>
                  </TextBox>
                  <TextBox Name="txttank5" Grid.Row="0" Grid.Column="6" Background="Yellow">
                    <TextBox.Text>
                      <Binding Path="tank5" UpdateSourceTrigger="PropertyChanged" Mode="TwoWay" ></Binding>
                    </TextBox.Text>
                  </TextBox>
                  <TextBox Name="txttotalOilStock" Grid.Row="0" Grid.Column="7" IsReadOnly="True" Focusable="False">
                    <TextBox.Text>
                      <Binding Path="total_oil_stock" UpdateSourceTrigger="PropertyChanged" Mode="OneWay" ></Binding>
                    </TextBox.Text>
                  </TextBox>
                  <Button Name="btnNew" Grid.Column="8" Content="New" Click="btnNew_Click"></Button>
                </Grid>
              </DataTemplate>
            </DataGridTemplateColumn.CellTemplate>
          </DataGridTemplateColumn>
        </DataGrid.Columns>     
      </DataGrid>



there are 5 textbox with name tank1,tank2,tank3,tank4,tank5.Now what i want is in 6th textbox name total i want summation of all tank from 1 to 5.Its like i want to call text change property of each five textbox which reflect changes made in textbox named total.

Did you get answer for this if so please email how to acheive this to rayuduak AT gmail.com

ray