Calculate the sum totals in a datatable.

var _result = from r1 in DT.AsEnumerable()
                         group r1 by new
                         {
                             RegionAsset = r1.Field<string>("Region Asset"),
                             Class = r1.Field<string>("Class"),


                         } into g
                         select new
                         {
                             RegionAsset = g.Key.RegionAsset,
                             Class = g.Key.Class,
                             TotalDividends = g.Sum(x => x.Field<int>("Dividends")),
                             TotalPnL = g.Sum(x => x.Field<int>("PnL")),
                             TotalBonus = g.Sum(x => x.Field<int>("Bonus"))

                         };

 using Excel = Microsoft.Office.Interop.Excel;
public static bool ExportDataTableToExcel(DataTable dt, string filepath)
       {
           Excel.Application oXL;
           Excel.Workbook oWB;
           Excel.Worksheet oSheet;

           try
           {
               // Start Excel and get Application object.
               oXL = new Excel.Application();

               // Set some properties
               oXL.Visible = true;
               oXL.DisplayAlerts = false;

               // Get a new workbook.
               oWB = oXL.Workbooks.Add(Missing.Value);

               // Get the Active sheet
               oSheet = (Excel.Worksheet)oWB.ActiveSheet;
               oSheet.Name = "Data";

               int rowCount = 1;
               foreach (DataRow dr in dt.Rows)
               {
                   rowCount += 1;
                   for (int i = 1; i < dt.Columns.Count + 1; i++)
                   {
                       // Add the header the first time through
                       if (rowCount == 2)
                       {
                           oSheet.Cells[1, i] = dt.Columns[i - 1].ColumnName;
                       }
                       oSheet.Cells[rowCount, i] = dr[i - 1].ToString();
                   }
               }

               oWB.SaveAs(filepath, Microsoft.Office.Interop.Excel.XlFileFormat.xlWorkbookDefault, Type.Missing, Type.Missing,
                           false, false, Microsoft.Office.Interop.Excel.XlSaveAsAccessMode.xlNoChange,
                           Type.Missing, Type.Missing, Type.Missing, Type.Missing, Type.Missing);
               oWB.Close();
               oWB = null;
               oXL.Quit();
           }
           catch
           {
               throw;
           }
           finally
           {
               GC.WaitForPendingFinalizers();
               GC.Collect();
               GC.WaitForPendingFinalizers();
               GC.Collect();
           }
           return true;
       }

var _result1 = (from r1 in DT.AsEnumerable()
                           group r1 by new
                           {
                               RegionAsset = r1.Field<string>("Region Asset"),
                               Class = r1.Field<string>("Class"),

                           } into g
                           select new
                           {
                               RegionAsset = g.Key.RegionAsset,
                               Class = g.Key.Class,
                               TotalDividends = g.Sum(x => x.Field<int>("Dividends")),
                               TotalPnL = g.Sum(x => x.Field<int>("PnL")),
                               TotalBonus = g.Sum(x => x.Field<int>("Bonus"))

                           }).ToList();


           var _result2 = (from r1 in DT.AsEnumerable()
                           group r1 by new
                           {
                               RegionAsset = r1.Field<string>("Region Asset")

                           } into g
                           select new
                           {
                               RegionAsset = g.Key.RegionAsset,

                               TotalDividends = g.Sum(x => x.Field<int>("Dividends")),
                               TotalPnL = g.Sum(x => x.Field<int>("PnL")),
                               TotalBonus = g.Sum(x => x.Field<int>("Bonus"))

                           }).ToList();

           DataTable DTResult = DT.Clone();
           foreach (var r1 in _result1)
           {
               foreach (DataRow dr in DT.AsEnumerable().Where(p => p.Field<string>("Region Asset") == r1.RegionAsset && p.Field<string>("Class") == r1.Class))
               {
                   DataRow dtrow = DTResult.NewRow();
                   dtrow.ItemArray = new String[] { r1.RegionAsset, r1.Class, dr.Field<int>("Dividends").ToString(), dr.Field<int>("Dividends").ToString(), dr.Field<int>("Dividends").ToString() };
                   DTResult.Rows.Add(dtrow);
               }
               DataRow dtrow1 = DTResult.NewRow();
               dtrow1.ItemArray = new String[] { r1.Class + "Total", "", r1.TotalDividends.ToString(), r1.TotalPnL.ToString(), r1.TotalBonus.ToString() };
               DTResult.Rows.Add(dtrow1);

           }