Private Function Rechne_Addition(rtfInhalt As String) As String
  Dim Splitted() As String
  Dim i As Single
  Dim Ergebnis As Long
 
  Splitted = Split(rtfInhalt, vbCrLf)
 
  For i = 0 To UBound(Splitted)
    If IsNumeric(Splitted(i)) Then
      Ergebnis = Ergebnis + CLng(Splitted(i))
    End If
  Next
 
  Rechne_Addition = Ergebnis
 
End Function
 
Private Sub Command1_Click()
  RichTextBox1.Text = RichTextBox1.Text & vbCrLf & Rechne_Addition( _
    RichTextBox1.Text)
End Sub