Public Function Convert_Week_number_in_date(ByVal weeknumber As Integer, ByVal _
  year As Integer) As Date
 
      Dim kw1Test As DateTime = DateSerial(year, 1, 1)
 
      For i As Integer = 1 To 7
         If kw1Test.DayOfWeek = DayOfWeek.Thursday Then
            kw1Test = kw1Test.AddDays(-3.0F)
            Exit For
         End If
         kw1Test = kw1Test.AddDays(1.0F)
      Next
 
      Return kw1Test.AddDays(7 * (weeknumber - 1))
 
   End Function

kw1Test.AddDays(7 * (weeknumber - 1))