The query title is
Questions answered by more than 3 50k users
But that doesn't describe what the query actually does. The query selects questions with three answers given by three distinct top n rated users. They happen to have more than 50k rep on that site, but that's a mere coincidence.
That can also be done by this query, containing only 1 subquery to ...
It seems you need a view or a temporary table. But it would be best for you to use a view instead.
so you might need to create a view first :
CREATE VIEW doc_Letters_view AS
[CentralDeptNo] = tempLetters.[CentralDeptNo]
, [IncomingNo] = tempLetters.[IncomingNo]
, [IncomingDate] = ...