How Sum Of Amount Column Datagrid And Bind To Total Textbox in Wpf and EntityFramework?

Here Sample code Get Sum of Amount in Final Textbox 

<GroupBox Grid.Row="3" Header="groupBox1" Height="87" HorizontalAlignment="Left" Margin="616,1,0,0" Name="groupBox1" VerticalAlignment="Top" Width="113">

                <Grid Width="102">

                    <TextBlock Height="15" HorizontalAlignment="Left" Margin="3,15,0,0" Name="textBlock4" Text="Add:" TextAlignment="Justify" VerticalAlignment="Top" />

                    <TextBlock Height="15" HorizontalAlignment="Left" Margin="1,44,0,0" Name="textBlock5" Text="Less:" TextAlignment="Justify" VerticalAlignment="Top" />

                    <telerik:RadWatermarkTextBox Height="23" Text="{Binding Path=AmountAdd,UpdateSourceTrigger=PropertyChanged}" HorizontalAlignment="Left" Margin="27,10,0,0" Name="txtAdd" VerticalAlignment="Top" Width="69" LostFocus="txtAdd_LostFocus" />

                    <telerik:RadWatermarkTextBox Height="23" Text="{Binding Path=AmountLess,UpdateSourceTrigger=PropertyChanged}" HorizontalAlignment="Left" Margin="27,39,0,0" Name="txtless" VerticalAlignment="Top" Width="69" LostFocus="txtless_LostFocus" />

                </Grid>

            </GroupBox>

            <telerik:RadWatermarkTextBox

            Height="23" Margin="563,93,0,0" Name="txtpaid"

            VerticalAlignment="Top" Grid.Row="3" Text="{Binding Path=Paid}" HorizontalAlignment="Left" Width="69" />

            <TextBlock Height="15" HorizontalAlignment="Left"

                   Margin="536,99,0,0" Name="textBlock7"

                   Text="Paid:" TextAlignment="Center"

                   VerticalAlignment="Top" Grid.Row="3" Width="29" />

            <TextBlock Height="15" HorizontalAlignment="Left"

                   Margin="648,98,0,0" Name="textBlock8"

                   Text="Total:" TextAlignment="Justify"

                   VerticalAlignment="Top" Width="32" Grid.Row="3" />

            <telerik:RadWatermarkTextBox Height="23" HorizontalAlignment="Right"

                                     Margin="0,93,12,0" Name="txttotal"

                                     VerticalAlignment="Top" Width="69"

                                     Grid.Row="3"

                                     Text="{Binding Path=Total,UpdateSourceTrigger=PropertyChanged}"/>

Code Behind

public partial class Inward :INotifyPropertyChanged

    {

        HTBookEntities book = new HTBookEntities();

      

        public Inward()

        {

            InwardDetails.AssociationChanged += new CollectionChangeEventHandler(InwardDetails_AssociationChanged);

        }

      

        private void InwardDetails_AssociationChanged(object sender, CollectionChangeEventArgs e)

        {

            if (e.Action == CollectionChangeAction.Add)

            {

                var idetail = (InwardDetail)e.Element;

                idetail.PropertyChanged += (s, a) =>

                {  

                    if (a.PropertyName == "Amount")

                    

                    {

                        SumAmount();

                    }

                };

            }

            SumAmount();

        }

        public void SumAmount()

        {

          

            int Sum = InwardDetails.Sum(i => i.Amount);

            Total = Sum + AmountAdd - AmountLess;

            NotifyPropertyChanged("Total");

        }

        partial void OnAmountAddChanged()

        {

            SumAmount();

        }

        partial void OnAmountLessChanged()

        {

            SumAmount();

        }

        public event System.ComponentModel.PropertyChangedEventHandler PropertyChanged;

        private void NotifyPropertyChanged(string propertyName)

        {

            if (PropertyChanged != null)

            {

                PropertyChanged(this, new System.ComponentModel.PropertyChangedEventArgs(propertyName));

            }

        }

    }