access parent value from collection property

Dim _ID As String
Dim _Rate As Decimal
Dim _Items As List(Of Item)

Property ID() As Integer
Get
Return _ID
End Get
Set(ByVal value As Integer)
_ID = value
End Set
End Property

Property Rate() As Decimal
Get
Return _Rate
End Get
Set(ByVal value As Decimal)
_Rate = value
End Set
End Property


Property Items() As List(Of Item)
Get
Return _Items
End Get
Set(ByVal value As List(Of Item))
_Items = value
End Set
End Property

End Class

Public Class HeaderInvoice

Dim _Id As Integer
Dim _Price As Decimal

Property ID() As Integer
Get
Return _Id
End Get
Set(ByVal value As Integer)
_Id = value
End Set
End Property

Property Price() As String
Get
Return _Price
End Get
Set(ByVal value As String)
_Price = value
End Set
End Property

ReadOnly Property LocalPrice() As Decimal
Get
***********
End Get

End Property
End Class

Public Class Item