I am assuming you want to sum the populations of all cities. I don't know how your classes are defined out so I mocked up an example of a similar problem. Maybe you can use it to help you:-
vbnet Code:
'
Public Class Form1
Private Sub Form1_Load(sender As System.Object, e As System.EventArgs) Handles MyBase.Load
Dim cities As New List(Of City)
cities.Add(New City("New York", 9092))
cities.Add(New City("POS", 3443))
cities.Add(New City("Kio", 9011))
cities.Add(New City("Loinitte", 4033))
'Sum the populations of all cities
Dim sumOfPop As Integer = Aggregate city In cities Into Sum(city.Population)
End Sub
End Class
Public Class City
Public Sub New(ByVal cityName As String, ByVal pop As Integer)
Me.CityName = cityName
Me.Population = pop
End Sub
Public Sub New()
End Sub
Public Property CityName As String
Public Property Population As Integer
End Class