\!h Find an engineer who has also been a producer, for the same amount of time:
SELECT producer_name, years FROM producer WHERE
(producer_name, years) IN -- where prod name and years matches eng name and years
(SELECT engineer_name, years FROM engineer);

\!h Equivalent as a join query to compare:
SELECT producer_name, producer.years FROM -- show prod names and years from prod and eng table
producer, engineer WHERE producer_name = engineer_name -- where prod name = eng name
AND producer.years = engineer.years -- and prod years = eng years