4 Week Rolling Average Based on Week Number

Hi,

I am trying to calculate a rolling 4 week average using the [Week Number] and [Year].  The measure that I need to average is [#Orders].  Ideally I would like this measure to calculate the average of the current [Week Number] which is 33 below, and the Previous 3 Weeks.  For example, see below.

# FourWeekTotal = CALCULATE(COUNTROWS('#Orders'),Filter(ALL('Merged Dataset'), 'Merged Dataset'[Week Number]=max('Merged Dataset'[Week Number])

|| 'Merged Dataset'[Week Number] = MAX('Merged Dataset'[Week Number])-1

|| 'Merged Dataset'[Week Number] = MAX('Merged Dataset'[Week Number])-2

|| 'Merged Dataset'[Week Number] = MAX('Merged Dataset'[Week Number])-3))

Above, is my attempt at calculating the last four week rolling average but I am currently getting the wrong count.  I have used a slicer to filter the calculation by [Year] for time  being untill I get the above correct.  Any help would be greatly appreciated as calculations using Working Weeks (Monday-Sunday) are not supported which is a nuisence.