user: Question: when was the number L6, with a fleet of Black Sea, launched?
Columns: ['Number', 'Name', 'Meaning', 'Fleet', 'Launched']
Types: ['text', 'text', 'text', 'text', 'text']
Sample row: ['L1', 'Leninets (Ленинец)', 'Follower of Lenin', 'Baltic', '28 February 1931']
SQL:

assistant: SELECT "Launched" FROM "Table" WHERE "Fleet" = 'Black Sea' AND "Number" = 'L6';