Last(ActiveSheet.Columns("C:C"))

ActiveSheet.PageSetup.PrintArea = "$B$2:I" & Last(ActiveSheet.Columns("B:B"))

Sub MPIndex_PrintArea()
     ActiveSheet.PageSetup.PrintArea = "$B$2:C" & Last(ActiveSheet.Columns("C:C"))
End Sub

Cells(LastNummer, 9).Select
    Set LastCel = Selection

Sub MPIndex_PrintArea()
Application.ScreenUpdating = False
Dim LastNummer As Integer
Dim LastCel As Range
    LastNummer = Last(ActiveSheet.Columns("C:C"))
    Cells(LastNummer, 9).Select
    Application.ScreenUpdating = False
    Set LastCel = Selection
    ActiveSheet.PageSetup.PrintArea = "$B$2:" & LastCel.Address
End Sub

Function Last(rng As Excel.Range) As Long

    On Error Resume Next
    Last = rng.Find(What:="*", _
                    After:=rng.Cells(1), _
                    Lookat:=xlPart, _
                    LookIn:=xlFormulas, _
                    SearchOrder:=xlByRows, _
                    SearchDirection:=xlPrevious, _
                    MatchCase:=False).Row
    On Error GoTo 0
End Function