How do I solve two proplems?

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Windows.Forms;

namespace NumberFiles
{
    static class Program
    {
        /// <summary>
        /// This is the MainForm of the application. For demonstration purposes this Form is "designed" "in code" - normally you would use
        /// the visual Forms-Designer to create your Form.
        /// </summary>
        public class MainForm : Form
        {
            ListBox m_lbNumbers;
            Label m_labelResult;

            public MainForm()
            {
                // Adjust some Form-Properties
                Width = 640;
                Height = 480;

                // Create a ToolStrip to let the user trigger the needed functions
                ToolStrip ts = new ToolStrip();
                // ... with some ToolButtons
                ToolStripButton buttonOpenFile = new ToolStripButton { Text = "Open File" };
                buttonOpenFile.Click += buttonOpenFile_Click;
                ToolStripButton buttonGetMaximumNumber = new ToolStripButton { Text = "Max. Nr." };
                buttonGetMaximumNumber.Click += buttonGetMaximumNumber_Click;
                ToolStripButton buttonCountMaximumNumber = new ToolStripButton { Text = "Count Max. Nr." };
                buttonCountMaximumNumber.Click += buttonCountMaximumNumber_Click;
                ToolStripButton buttonCalculateAverage = new ToolStripButton { Text = "Calculate Average" };
                buttonCalculateAverage.Click += buttonCalculateAverage_Click;
                ToolStripButton buttonGetMaximumNumberOfSelectedNumbers = new ToolStripButton { Text = "Max. Nr. from Selection" };
                buttonGetMaximumNumberOfSelectedNumbers.Click += buttonGetMaximumNumberOfSelectedNumbers_Click;
                ts.Items.AddRange(new ToolStripItem[] { buttonOpenFile, buttonGetMaximumNumber, buttonCountMaximumNumber, buttonCalculateAverage, buttonGetMaximumNumberOfSelectedNumbers });

                // Create a ListBox to show the numbers (with enabled multi selection)
                m_lbNumbers = new ListBox { Dock = DockStyle.Fill, SelectionMode = SelectionMode.MultiExtended };

                // Create a Label to show the calculation results (with some initial text)
                m_labelResult = new Label { Dock = DockStyle.Bottom };

                // Add the Controls to this Form (order is important for the docking logic!)
                Controls.Add(m_lbNumbers);
                Controls.Add(ts);
                Controls.Add(m_labelResult);
            }

            void buttonOpenFile_Click(object sender, EventArgs e)
            {
                // Let the user choose a file
                OpenFileDialog ofd = new OpenFileDialog { Title = "Select a file containing numbers" };
                if (ofd.ShowDialog() == System.Windows.Forms.DialogResult.OK)
                {
                    // Read all lines from the text file selected by the user containing the numbers
                    string[] astrLines = File.ReadAllLines(ofd.FileName);

                    // Delete all current numbers from the list
                    m_lbNumbers.Items.Clear();

                    // Add the just read new numbers to the list 
                    foreach (string strLine in astrLines)
                        m_lbNumbers.Items.Add(Convert.ToInt32(strLine));
                }
            }

            // We use some LINQ for the calculations to make our live easy :-) 

            void buttonGetMaximumNumber_Click(object sender, EventArgs e)
            {
                IEnumerable<int> numbers = m_lbNumbers.Items.Cast<int>();
                int iMaxNr = numbers.Max();
                m_labelResult.Text = String.Format("Maximum number was {0}", iMaxNr);
            }

            void buttonCountMaximumNumber_Click(object sender, EventArgs e)
            {
                IEnumerable<int> numbers = m_lbNumbers.Items.Cast<int>();
                int iMaxNr = numbers.Max();
                int iCount = numbers.Count(n => n == iMaxNr);
                m_labelResult.Text = String.Format("Maximum number was {0}, it appears {1} times.", iMaxNr, iCount);
            }

            void buttonCalculateAverage_Click(object sender, EventArgs e)
            {
                IEnumerable<int> numbers = m_lbNumbers.Items.Cast<int>();
                double dAverage = numbers.Average();
                m_labelResult.Text = String.Format("Average of all numbers is {0}", dAverage);
            }

            void buttonGetMaximumNumberOfSelectedNumbers_Click(object sender, EventArgs e)
            {
                if(m_lbNumbers.SelectedItems.Count > 0)
                {
                    IEnumerable<int> numbers = m_lbNumbers.SelectedItems.Cast<int>();
                    int iMaxNr = numbers.Max();
                    m_labelResult.Text = String.Format("Maximum number of the selected numbers was {0}", iMaxNr);
                }
                else
                {
                    m_labelResult.Text = "No numbers selected, select at least two numbers";
                }
            }
        }

        [STAThread]
        static void Main()
        {
            Application.EnableVisualStyles();
            Application.SetCompatibleTextRenderingDefault(false);
            Application.Run(new MainForm());
        }
    }
}