<$list filter="[tag[test]sort[week]last[]]">
Current Week: {{!!title}}, Value: {{!!R}}
</$list>
Notes:
tag[test] gets a list of all the tiddler titles that are tagged with test
sort[week] sorts the list of titles in ascending order by the value of their week field. Note that this does NOT result in a list of week numbers. It just uses the week numbers to sort the list of titles.
last[] keeps only the last title, which will be the current week, since it has the highest week number
The $list widget sets the currentTiddler variable to the result of the filter, so that within the content of the $list widget you can use simple transclusion syntax to show the values of the title and R fields.