If you want to work with columns you don't want to use a listbox. Here's a better way. Add a listview and a command button to the form and

Code:
Option Explicit

Private Sub Command1_Click()

    Dim lngIndex As Long
    Dim lngTotal As Long
    
    For lngIndex = 1 To ListView1.ListItems.Count - 1
        lngTotal = lngTotal + ListView1.ListItems(lngIndex).SubItems(2)
    Next
    
    MsgBox "Average of column3 is " & lngTotal / ListView1.ListItems.Count
End Sub

Private Sub Form_Load()

    Dim strParts() As String
    Dim FF As Integer
    Dim strLine As String
    Dim lngIndex As Long
    Dim bFirst As Boolean

    ListView1.View = lvwReport
    
    FF = FreeFile
    Open "C:\temp\test.txt" For Input As FF
    
    bFirst = True
    Do While Not EOF(FF)
        Line Input #FF, strLine
        strParts = Split(strLine, ",")
        For lngIndex = 0 To UBound(strParts)
            If bFirst Then
                ListView1.ColumnHeaders.Add , , strParts(lngIndex), 500
            Else
                If lngIndex = 0 Then
                    ListView1.ListItems.Add , , strParts(lngIndex)
                Else
                    ListView1.ListItems(ListView1.ListItems.Count).SubItems(lngIndex) = strParts(lngIndex)
                End If
            End If
        Next
        bFirst = False
    Loop
    
    Close FF
End Sub