Generar numeros aleatorios en windows form

Public Class Form2
    Private Sub Form2_Load(sender As System.Object, e As System.EventArgs) Handles MyBase.Load
        Dim r As New Random
        For i = 1 To 15
            Dim num As Integer = r.Next(10, 99)
            ListBox1.Items.Add(num)
        Next
        Label1.Text = "Suma: " & contar(ListBox1)
    End Sub
    Function contar(lista As ListBox) As Integer
        Dim s As Integer = 0
        For Each num In lista.Items
            s = s + num
        Next
        Return s
    End Function
End Class