You can't just get a specific line. To get line N you must then you have to read every line before that and, if you don't need them, just discard them.
vb.net Code:
  1. Private Function GetLineFromFile(filePath As String, lineNumber As Integer) As String
  2.     Using reader As New IO.StreamReader(filePath)
  3.         Dim line As String = Nothing
  4.  
  5.         For i = 1 To lineNumber
  6.             line = reader.ReadLine()
  7.  
  8.             If line = Nothing Then
  9.                 'No more lines
  10.                 Exit For
  11.             End If
  12.         Next
  13.  
  14.         Return line
  15.     End Using
  16. End Function