user: ### NOW ANSWER:
Question: What is the 1991 when 1997 is 18?
Columns: ['Tournament', '2000', '1999', '1998', '1997', '1996', '1995', '1994', '1993', '1992', '1991']
Types: ['text', 'text', 'text', 'text', 'text', 'text', 'text', 'text', 'text', 'text', 'text']
Sample row: ['Australian Open', '2R', 'QF', '3R', 'QF', '2R', 'A', '1R', '2R', '4R', 'A']
SQL:

assistant: SELECT "1991" FROM "Table" WHERE "1997" = '18';