Table: mytilene_ships
Columns: ship_name
year
length
width
passengers
vessels
speed

Question: What is the average speed for ships before 1974 with over 1.73 passengers?
SQL: SELECT AVG("speed") FROM mytilene_ships WHERE "year" < 1974 AND "passengers" > 1.73

Question: How many vessels are named aqua jewel?
SQL: SELECT COUNT("vessels") FROM mytilene_ships WHERE "ship_name" = 'aqua jewel'