return the end of week date using month and week number

You can easily achieve with a calendar table, if you have one.

or else use below..

DECLARE @WeekNo int= 14, @YearMonth int=201401

SELECT DATEADD(wk,@WeekNo-1,DATEADD(yy,LEFT(@YearMonth, 4)-1900,0)) AS WeekStart,
DATEADD(wk,@WeekNo,DATEADD(yy, LEFT(@YearMonth, 4)-1900,0)) AS WeekEnd

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