Reporting Services :: SSRS Linked Report Based On Calculated Field From Main Report

How do I get data on my linked report based on my grouped subtotal and grand total from the main report.  The subtotal and grand total are calculated columns.

I have a 3 columns in my matrix in the SSRS summary report. Actn_COAST, ActnCITY and NumbOfAccts.  

The following is code for my summary report.  The results are shown below.

SELECT Distinct ActnCITY, Count(ACCT) as NumbOfAccts,
CASE WHEN ActnCITY in ('NY', 'OH', IN, 'NJ', 'SC', 'NC') THEN 'EAST COAST'
WHEN ActnCITY IN ('CA'. 'NV', 'UT', 'WA', 'OR') THEN 'WEST COAST'
ELSE 'OTHER'
END AS Actn_COAST

FROM tbl1
where ACTNDATE between @STARTDT and @EndDT

Code for my detail report contains the following SQL

SELECT * FROM tbl1 where ACTNDATE between @STARTDT and @EndDT AND @ActnCITY = ActnCITY

I have linked my report based on the NumbOfAccts column.  I am able to get data if I click any of the NumbOfAccts values related to the state I want.  However when I am not sure how to make the subtotal and grand total work.  I want when I click on the subtotal of either coast, I should be able to see records of that coast e.g., if I select 37 I should be able to see all the records in East Coast.  If I click on the Grand Total, I only want data related to those 2 coasts.