LINQ to Dataset - Subquery

I am writing a query in LINQ and I am stuck with the subquery part.  

Original SQL:
SELECT　account,　bal_date,　ccy,　balance
FROM Balance A
WHERE
A.balance < 0 AND
A.date = 　( SELECT
　　　　　　　　MIN(B.bal_date)
　　　　　　　　FROM　Balance B
　　　　　　　　WHERE　balance < 0 AND　
                     A.account = B.account AND
                     A.ccy = B.ccy
　　　　　　  )

LINQ:
Dim query = From bal In dt.AsEnumerable() _
                    Where bal.Item("balance") < 0 _
                    And bal.Item(“bal_date”) = ( subquery? )
                    Select bal


I learned that if I do Grouping by account and currency, I can get the MIN (bal_date),  but the I need the balance of such date, not the  MIN(balance) or MAX(balance).

I would appreciate if I get some help from Experts...