private void invoiceAmountComboBox_SelectionChanged(object sender, SelectionChangedEventArgs e)
        {
            ///Disable other drop down menu's if this is selected
            if (invoiceDateComboBox.IsEnabled)
            {
                invoiceIDComboBox.IsEnabled   = false;
                invoiceDateComboBox.IsEnabled = false;
            }

            ///The two other drop down menu's will be disabled when this is being used

            ///When selcted, this combo box will show a drop down list with invoice Total Charge
            ///The user will be able to highlight/select an TotalCharge and it will be recieved
            ///by the dataGrid1 to show that specific invoice only
            ///

            Console.Write("textbox Value: " + invoiceAmountComboBox.SelectedItem.ToString());

            //get query needed find invoice
            String sQuery = mydb.SelectTotalCharge(invoiceAmountComboBox.SelectedItem.ToString());

            //datatable used to fget table data.
            dt = db.FillSqlDataTable(sQuery);

            //fill the datagrid
            invoiceGrid1.ItemsSource = dt.DefaultView;
        }