Use DAO to write summary of one table into another

I want to sum all values in the profit field of table T and write it
to Table Sys.

I have instantiated object d as a DAO database object and various
other UPDATE queries are running fine, but only when I calculate from
values in the same table.  I just can't seem to find the right syntax.

d.Execute "UPDATE Sys SET Sys.NetProfit = SUM[T]![Profit];"

Beyond this, I would like to restrict the sum of profits to only those
whose row has a particular value in another field in T.

Any thoughts?  Any alternative paths?