List out the account numbers of clients who are youngest and have highest average salary?
If the person A's birthdate < B's birthdate, it means that person B is younger than person A; A11 refers to average salary
SELECT T1.account_id FROM account AS T1 INNER JOIN district AS T2 ON T1.district_id = T2.district_id WHERE T2.district_id = ( SELECT district_id FROM client ORDER BY birth_date DESC LIMIT 1 ) ORDER BY T2.A11 DESC LIMIT 1