if you can use stored procs, I would say add a column to the result set for the year/week number and use the DATEDIFF() to calculate the nubmer of days from a given start date (which if is calendar years, could be 1/1/YEAR(payableDate)).
Now that you have the number of days, for simplicity, add the 7 - (dayCount mod 7) so that all the days are in increments of 7, then divide them all by 7 to get the week number.
You might be able to do this in CR, but it would be difficult as you need to alter a column (or change the data in it so that it works for you)...stored procs are always the easiest.
HTH
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