SELECT
    A.hacker_id
    , name
FROM
    Hackers A
    INNER JOIN Submissions B
        ON B.hacker_id = A.hacker_id
    INNER JOIN Challenges C
        ON C.challenge_id = B.challenge_id
    INNER JOIN Difficulty D
        ON D.difficulty_level = C.difficulty_level
        AND D.score = B.score
GROUP BY
    hacker_id
    , name
HAVING
    COUNT(*) > 1
ORDER BY
    COUNT(*) DESC
    , hacker_id