Subquery in Columns/Fields

I tried to post earlier so I apologize if my other post finally comes up and there are duplicates.

I am fairly new to SQL and am having problems trying to put together a subquery. I have two queries that have so much in common that it seems like an easy join. My problem is that each query is looking at each line of each transaction for a certain line object (111 is for purchases and 444 is for markdowns). Right now I am running the two and merging outside my current application. I'm not sure if I can use a SELECT statement (using the Markdowns statement as a field in the Purchases statement) in the columns/fields portion but I have tried and failed at that.

Ideally I'd like to be able to take the markdowns and divide them by the purchases to get the % discount and filter only those that are greater than 60% discount but right now I would be happy if I could get a solid subquery going. Below is are the two SQL statements I am running.

SELECT a.store_no as Field_a, a.transaction_date as Field_b, a.transaction_no as Field_c, a.register_no as Field_d, a.cashier_no as Field_e, SUM(b.gross_line_amount) as Field_f
FROM DevDB.transaction_header a, DevDB.transaction_line b, DevDB.store c
WHERE a.transaction_id=b.transaction_id
AND a.store_no=c.store_no
AND (a.transaction_date Between {{From date is *}} and {{To date is *}}
AND b.line_object = 111
AND b.line_action = 11)
AND EXISTS (SELECT bb.gross_line_amount
FROM DevDB.transaction_header aa, DevDB.transaction_line bb, DevDB.store cc
WHERE aa.transaction_id=bb.transaction_id
AND aa.store_no = cc.store_no
AND aa.transaction_id = a.transaction_id
AND (aa.transaction_date Between {{From date is *}} and {{To date is *}}
AND bb.line_object = 444
AND bb.line_action = 44))
GROUP BY a.store_no,a.transaction_date,a.transaction_no,a.r egister_no,a.cashier_no

SELECT a.store_no as Field_a, a.transaction_date as Field_b, a.transaction_no as Field_c, a.register_no as Field_d, a.cashier_no as Field_e, SUM(b.gross_line_amount) as Field_f
FROM DevDB.transaction_header a, DevDB.transaction_line b, DevDB.store c
WHERE a.transaction_id=b.transaction_id
AND a.store_no=c.store_no
AND (a.transaction_date Between {{From date is *}} and {{To date is *}}
AND b.line_object = 444
AND b.line_action = 44)
GROUP BY a.store_no,a.transaction_date,a.transaction_no,a.r egister_no,a.cashier_no

Thank you to any help you can give me.