Now the question is revert, we need the first day of the week, based on a weeknumber and a year. On the internet, there were some samples, but that were to much lines of codes.
So, this is a short version:
Private Function GetFirstDayOfTheWeek(year As integer, week As integer) As Date
Dim January4th As Date = DateSerial(year, 1, 4)
Dim January1th As Date = New Date(year), 1, 1)
Dim DayOfInterest As Date
Dim FirstDayWeek1 As Date
FirstDayWeek1 = January4th.AddDays(1).AddDays(-Weekday(January4th, FirstDayOfWeek.Monday))
DayOfInterest = January1th.AddDays(((week - 1) * 7 - DateDiff(DateInterval.DayOfYear, FirstDayWeek1, January1th, FirstDayOfWeek.Monday, FirstWeekOfYear.FirstFourDays)))
If you need some other date calculation routines, just let me know.