How to reference a variable (variable does not exist in the current context) in a USING clause in C#?

I am developing a C# application in VS2010.

In the following code, how could I resolve the error:

Error      1      The name 'banknum' does not exist in the current context      \\msad\root\na\ny\users\zimmermj\visual studio 2010\Projects\SMRWebForm\SMRWebForm\SMRWebForm1.aspx.cs      71      29      SMRWebForm
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using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.IO;
using System.Text;
using System.Text.RegularExpressions;

namespace SMRWebForm
{
    public partial class SMRWebForm1 : System.Web.UI.Page
    {
        protected void Page_Load(object sender, EventArgs e)
        {
            List<string> ReadFile = File.ReadAllLines(@"U:\SnrMgtRpt\OI_DRS.txt").ToList();

            foreach (string line in ReadFile)
            {                
                string banknum = line.Substring(0, 4);
                string transDtYR = line.Substring(4, 4);
                string transDtMnth = line.Substring(8, 2);                
            }

            const string myInsert = "INSERT INTO tbl_SMR_OI_WRS (bankNum, transYR, transMnth, transDay, clientAcct, transType, recordNum, recordNum, processYr) VALUES ('{0}', {1}, {2}, {3}, '{4}', '{5}', '{6}', {7}, '{8}')";
           
            const string connString = "Data Source=FSMSAPPSSQLDEV,7003;Initial Catalog=UDLPWM;User ID =UDLClient;PWD=Call_Me_UDLA;";

            using (SqlConnection conn = new SqlConnection(connString))
            {
                conn.Open();
                StringBuilder sb = new StringBuilder();
                string[] sArray = new string[9];
                sArray[0] = banknum;      <-------------------  error
                sArray[1] = transDtYR;
                sArray[2] = transDtMnth;
                sb.AppendFormat(myInsert, sArray);
                string cmdText = sb.ToString();
                using (SqlCommand cmd = new SqlCommand(connString))
                {
                   int rowsAffected = cmd.ExecuteNonQuery();
                }
            }
        }
    }
}