Allora puoi prendere spunto da

codice:
    Dim issposato As Boolean = False

    Public Property Sposato() As Boolean
        Get
            Return issposato
        End Get
        Set(ByVal value As Boolean)
            issposato = value
        End Set
    End Property

    Public ReadOnly Property Detrazioni() As Integer
        Get
            If issposato Then
                Return 690
            Else
                Return 0
            End If
        End Get
    End Property