I have a formula that looks up data in a sheet using Vlookup, every week the
formula changes as the week number changes.

The tab to look for data has a tab name of wk## and thus the forumla for
week 28 looks like this

=VLOOKUP(O2,wk28!A4:L3000,12,FALSE)

How can I substitue the wk28 tab number in the formual for a cell reference
that contains the text "wk28" ?

This will save me modifying forumlas on weekly basis.

Thanks