Una cosa così ?

codice:
    Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
        If Not IsPostBack Then
            Dim numero1 As Integer
            Dim rnd1 As New Random
            numero1 = rnd1.Next(0, 100)
            Session("numero1") = numero1

            Dim numero2 As Integer
            Dim rnd2 As New Random
            numero2 = rnd2.Next(0, 30)
            Session("numero2") = numero2

            lb1.Text = Session("numero1").ToString
            lb2.Text = Session("numero2").ToString
        End If
    End Sub

    Protected Sub bottone_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles bottone.Click
        If CInt(tb.Text) = CInt(Session("numero1")) + CInt(Session("numero2")) Then
            Response.Write("Corretto")
        End If
    End Sub