dropdown list vba

Hi all i currently using a vba which allows the dropdown list to display a value but return a different value when selected.

Private Sub Worksheet_Change(ByVal Target As Range)
'Updateby Extendoffice
    selectedNa = Target.Value
    If Target.Column = 9 Then
        selectedNum = Application.VLookup(selectedNa, ActiveSheet.Range("dropdown"), 2, False)
        If Not IsError(selectedNum) Then
            Target.Value = selectedNum
        End If
    End If
End Sub

this only works for dropdown list in column 9 but i need multible columns! the columns i need are 9, 16, 23 and 32

any help is much appreciated