That took a lot of thinking

It took a while to figure out that I needed to include every table I
used in the query in the 'from' clause. From there, it told me 'select
city' was ambiguous, so 'agents.city' did the trick.
I don't like renaming tables

It does not seem intuitive at all (at least, in this context). I feel
like it would be more appropriate to use a subquery in place of the last
line of the query in order to avoid creating aliases.
I didn't expect any rows to result from this query.

That took me by surprise.
I liked that one. It was satisfying.
That one felt too easy, so it might be wrong.
No. 6 WAS too easy.

Although, the fact that I couldn't just use 'city' in the select clause
bothers me. It feels asymmetrical to put 'agents.city' when it could
also be 'customers.city'
No. 7 was easy enough.

Just needed some googling to find the 'min' function