C#

xlWorkSheet.Range[ws.Cells[1, 1], ws.Cells[1, 4]].Merge();

private void Form1_Load(object sender, EventArgs e)
{
    string Arquivo = @"D:\Diversos\Antares\Relatório.xlsx";
    Excel.Application xlApp;
    Excel.Workbook xlWorkBook;
    Excel.Worksheet xlWorkSheet;
    object misValue = System.Reflection.Missing.Value;

    //Cria uma planilha temporária na memória do computador
    xlApp = new Excel.Application();
    xlWorkBook = xlApp.Workbooks.Add(misValue);
    xlWorkSheet = (Excel.Worksheet)xlWorkBook.Worksheets.get_Item(1);
    xlWorkSheet.Range[xlWorkSheet.Cells[1, 1], xlWorkSheet.Cells[1, 4]].Merge();
    xlWorkSheet.Visible = XlSheetVisibility.xlSheetVisible;

    //incluindo dados
    xlWorkSheet.Cells[1, 1] = "Dados do cliente:";
}

xlWorkSheet.Visible = XlSheetVisibility.xlSheetVisible;

xlApp.Visible = true;  // make the application visible
xlWorkSheet.Visible = XlSheetVisibility.xlSheetVisible; // select the current worksheet

for(int i = 0; i < dt.Rows.Count; i++)

Action<int> DoSomething = (i) => dt.Rows[i][3];   // Create an action with 'i' as an argument and dt as an enclosing scope variable
for (int i = 0; i < dt.Rows.Count; i++
   DoSomething(i);  // Call the action passing the current value of i as a parameter

dt.Rows[i][7].ToString()

Quote:

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class ActivityTimeSum
    {
        public string settings { get; set; }
        public string dataTableName { get; set; }
        public DataTable selectDT { get; set; }
        public CheckEdit checkBox1 { get; set; }
        public CheckEdit checkBox2 { get; set; }
        public CheckEdit checkBox3 { get; set; }
        public CheckEdit checkBox4 { get; set; }

        Dictionary<string, int> myDic = new Dictionary<string, int>();
        List<string> keys = new List<string>();
        List<int> values = new List<int>();
        List<CheckEdit> checkBoxes = new List<CheckEdit>();
        List<string> selectedCheckBox = new List<string>();

        public Dictionary<string, int> CalculateTime()
        {
            checkBoxes.Add(checkBox1);
            checkBoxes.Add(checkBox2);
            checkBoxes.Add(checkBox3);
            checkBoxes.Add(checkBox4);

            foreach (var c in checkBoxes)
            {
                if (c.Checked)
                {
                    selectedCheckBox.Add(c.Tag.ToString());
                }
            }
            for (int i = 0; i < selectDT.Rows.Count; i++)
            {
                switch (selectedCheckBox.Count)
                {
                    case 1:
                        keys.Add(selectDT.Rows[i][Int32.Parse(selectedCheckBox[0])].ToString());
                        break;
                    case 2:
                        keys.Add(string.Join(", ", selectDT.Rows[i][Int32.Parse(selectedCheckBox[0])].ToString(), 
                            selectDT.Rows[i][Int32.Parse(selectedCheckBox[1])].ToString()));
                        break;
                    case 3:
                        keys.Add(string.Join(", ", selectDT.Rows[i][Int32.Parse(selectedCheckBox[0])].ToString(),
                            selectDT.Rows[i][Int32.Parse(selectedCheckBox[1])].ToString(), selectDT.Rows[i][Int32.Parse(selectedCheckBox[2])].ToString()));
                        break;
                    case 4:
                        keys.Add(string.Join(", ", selectDT.Rows[i][Int32.Parse(selectedCheckBox[0])].ToString(),
                            selectDT.Rows[i][Int32.Parse(selectedCheckBox[1])].ToString(), selectDT.Rows[i][Int32.Parse(selectedCheckBox[2])].ToString(),
                            selectDT.Rows[i][Int32.Parse(selectedCheckBox[3])].ToString()));
                        break;
                }
                values.Add(Int32.Parse(selectDT.Rows[i][11].ToString()));
            }

            for (int i = 0; i < selectDT.Rows.Count; i++)
            {
                if (myDic.ContainsKey(keys[i]))
                {
                    myDic[keys[i]] += values[i];
                }
                else
                {
                    myDic[keys[i]] = values [i];
                }
            }
            return myDic;

List<string> words = source.Split(',').Select(s => s.Trim()).ToList();

string.Split(", ", StringSplitOptions.None);