How to Calculate the Total of a Table Particular Column Row Values in C#.

Worksheet.Cells[10, 6].Formula =
        "=Sum(" + Worksheet.Cells[5, 26].Address + 
        ":" + Worksheet.Cells[rowIndex, 26].Address + ")";

 int sum = Convert.ToInt32(dt.Compute("SUM(Salary)", "EmpId > 10));
Or 
int sum = dt.AsEnumerable().Where(row => row.Field<int>("EmpId") > 2).Sum(row => row.Field<int>("Salary"));

Dim dt As New DataTable()
dt.Columns.AddRange(New DataColumn(2) {New DataColumn("EmplId", GetType(Integer)),
New DataColumn("Name", GetType(String)),  
New DataColumn("Salary", GetType(Integer))})
dt.Rows.Add(1, "Mohan", 43000)
dt.Rows.Add(2, "Sunil", 32000)
dt.Rows.Add(3, "Rani", 18000)
dt.Rows.Add(3, "Suzanne ", 18500)

select SUM(cost) from tablename

protected void Page_Load(object sender, EventArgs e)
{
    if (!this.IsPostBack)
    {
        this.BindGrid();
    }
}

 private void BindGrid()
{
    string query = "SELECT TOP 30 OrderID,";
    query += "(SELECT ProductName FROM Products WHERE ProductID = details.ProductId) ProductName,";
    query += "(Quantity * UnitPrice) Price";
    query += " FROM [Order Details] details";
    query += " ORDER BY OrderID";
    string constr = ConfigurationManager.ConnectionStrings["constr"].ConnectionString;
    using (SqlConnection con = new SqlConnection(constr))
    {
        using (SqlCommand cmd = new SqlCommand(query))
        {
            using (SqlDataAdapter sda = new SqlDataAdapter())
            {
                cmd.Connection = con;
                sda.SelectCommand = cmd;
                using (DataTable dt = new DataTable())
                {
                    sda.Fill(dt);
                    GridView1.DataSource = dt;
                    GridView1.DataBind();

                    //Calculate Sum and display in Footer Row
                    decimal total = dt.AsEnumerable().Sum(row => row.Field<decimal>("Price"));
                    GridView1.FooterRow.Cells[1].Text = "Total";
                    GridView1.FooterRow.Cells[1].HorizontalAlign = HorizontalAlign.Right;
                    GridView1.FooterRow.Cells[2].Text = total.ToString("N2");
                }
            }
        }
    }
}