How to create expression for finding selection of weeks?

[#1]

hello there,

I am planning to show the sum of sale amount for a table of weeks.

I have a table of week numbers . I want to find the sum amount for the selection of weeks I choose.

So I created 2 variables.

vminWeek= min(week_num)

vmaxWeek.= max(week_num)

How do I calculate the sum between these 2 weeks? Please help.

[#2]

Is this correct ?? sum({<ad_wk_num = {'>=$(=prev_wk)<=$(=prev_wk)'}>}sale_amt)