How to add new row showing Grand Total ?

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C#

MS-Excel

doubt in window application.how to insert header,logo in starting position in excel .after filling datatable value in excel,how to add new row showing Grand Total in one cell and sum of Total amt...

i have created excel report using RKLib.ExportData;

string strq="Select query";
                DataSet ds1 = obj.GetDataset(strq);       
                

              //   Get the datatable to export			
               System.Data.DataTable dtEmployee = ds1.Tables[0].Copy();              

                 //Export all the details to Excel

                RKLib.ExportData.Export objExport = new RKLib.ExportData.Export("Win");
                int[] iColumns = { 0 };
                string[] Headers = {"Total amt"};
                string str = ConfigurationSettings.AppSettings["Potkirdpath"];
                string filename = "path"
                string date = DateTime.Today.Year.ToString() + DateTime.Today.ToString("MM") + DateTime.Today.ToString("dd");
                string time = System.DateTime.Now.ToString("ddMMyyyy_hhmmsstt");

                if (!Directory.Exists(str))
                {
                    Directory.CreateDirectory(str);

                }
                string fullPath = str + "\\" + filename + "-" + time.ToString() + ".xls";               
                objExport.ExportDetails(dtEmployee, iColumns, Headers, Export.ExportFormat.Excel, fullPath);

my excel report is created.i have 1 doubt how to insert header,logo in starting position.after filling dtemployee in excel.how to add new row showing Grand Total in one cell and sum of Total amt in one cell.