That's complicated, because "week number" doesn't relate to a fixed start date: January the first of a particular year can be in week 50, 51, or 52 of the previous year, or week 1 of the current year - and depending on when that is controls what date the current week starts with.
https://en.wikipedia.org/wiki/ISO_week_date[
^]
What I would do set up a table which indexes by year and provides the start date for week 1 of each year, and then add the week number times 7 to that to get the actual date.
Or you could follow the algorithm in the link!
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