How to add formulas in cells in J#.NET

package Tutorial11;

/* ----------------------------------------------------------
 * Tutorial 11
 * 
 * This tutorial shows how to create an Excel file in J# that
 * has a cell that contains SUM formula for a range of cells.
 * ------------------------------------------------------- */

import System.*;
import EasyXLS.*;

public class Tutorial11
{
    public Tutorial11()
    {
    }

    /** @attribute System.STAThread() */
    public static void main(String[] args)
    {
        Console.WriteLine("Tutorial 11\n----------\n");

        // Create an instance of the class that exports Excel files
        ExcelDocument workbook = new ExcelDocument();
            
        // Create a sheet
        workbook.easy_addWorksheet("Formula");

        // Get the table of data for the sheet, add data in sheet and the formula
        ExcelTable xlsTable = ((ExcelWorksheet)workbook.easy_getSheet("Formula")).easy_getExcelTable();
        xlsTable.easy_getCell("A1").setValue("1");
        xlsTable.easy_getCell("A2").setValue("2");
        xlsTable.easy_getCell("A3").setValue("3");
        xlsTable.easy_getCell("A4").setValue("4");
        xlsTable.easy_getCell("A6").setValue("=SUM(A1:A4)");
                
        // Export Excel file
        Console.WriteLine("Writing file C:\\Samples\\Tutorial11 - formulas in Excel.xlsx.");
        workbook.easy_WriteXLSXFile("C:\\Samples\\Tutorial11 - formulas in Excel.xlsx");

        // Confirm export of Excel file
        String sError = workbook.easy_getError();
        if (sError.Equals(""))
            Console.Write("\nFile successfully created. Press Enter to Exit...");
        else
            Console.Write("\nError encountered: " + sError + "\nPress Enter to Exit...");

        // Dispose memory
        workbook.Dispose();

        Console.ReadLine();
    }
}