Public Class Calc

    Public Delegate Sub RisultatoEventHandler(ByVal sender As Object, ByVal e As RisultatoEventArgs)
    Public Event OnRisultato As RisultatoEventHandler

    Public Overridable Sub Addizione(ByVal a As Integer, ByVal b As Integer)
        Dim e As New RisultatoEventArgs
        e.Risultato = a + b
        RaiseEvent OnRisultato(Me, e)
        Exit Sub
    End Sub

    Public Overridable Sub Sottrazione(ByVal a As Integer, ByVal b As Integer)
        Dim e As New RisultatoEventArgs
        e.Risultato = a - b
        RaiseEvent OnRisultato(Me, e)
        Exit Sub
    End Sub

End Class

Public Class RisultatoEventArgs
    Inherits EventArgs

    Public Risultato As Integer
End Class