I am so sorry guys,

Mallycat's Code is great, but the Char(34) could be replaced with """ instead of just "

I checked out your concern trickyricky and, yes, you are right. The amended Code should look like this:

Private Sub Worksheet_Change(ByVal Target As Range)
     On Error GoTo exit_here
    If Intersect(Target, Range("L7:N13")) Then
        If IsNumeric(Target.Formula) Then
            Select Case Target.Column
                Case Is = 12
                        Cells(Target.Row, 13).Formula = "=IF(" & Target.Address & "<>" & """ & """ & "," & Target.Address & "*$L$2," & """ & """ & ")"
                        Cells(Target.Row, 14).Formula = "=IF(" & Target.Offset(0, 1).Address & "<>" & """ & """ & "," & Target.Offset(0, 1).Address & "/$M$4,0)"
                Case Is = 13
                        Cells(Target.Row, 12).Formula = "=IF(" & Target.Address & "<>" & """ & """ & "," & Target.Address & "/$L$2," & """ & """ & ")"
                        Cells(Target.Row, 14).Formula = "=IF(" & Target.Address & "<>" & """ & """ & "," & Target.Address & "/$M$4,0)"
                Case Is = 14
                        Cells(Target.Row, 12).Formula = "=IF(" & Target.Offset(0, -1).Address & "<>" & """ & """ & "," & Target.Offset(0, -1).Address & "/$L$2," & """ & """ & ")"
                        Cells(Target.Row, 13).Formula = "=IF(" & Target.Address & "<>" & """ & """ & "," & Target.Address & "*$M$4," & """ & """ & ")"
            End Select
        End If
    End If
exit_here:

End Sub