Identify the number of posts and comments left by the user, who has the latest created user account.
the latest created user account refers to MAX(CreationDate);
SELECT COUNT(T2.Id) FROM users AS T1 INNER JOIN posts AS T2 ON T1.Id = T2.OwnerUserId INNER JOIN comments AS T3 ON T3.PostId = T2.Id ORDER BY T1.CreationDate DESC LIMIT 1