user: Question: What format is after 1991 and has a Catalog Number of 81868?
Columns: ['Year', 'Title', 'Format', 'Studio', 'Release Date', 'Copyright Information', 'Catalog Number']
Types: ['real', 'text', 'text', 'text', 'text', 'text', 'text']
Sample row: [1986.0, 'Callanetics: 10 Years Younger In 10 Hours', 'VHS/Betamax', 'MCA', 'November 4, 1986', 'Callan Productions Corp.', '80429 / BTA80429']
SQL:

assistant: SELECT "Format" FROM "Table" WHERE "Year" > 1991.0 AND "Catalog Number" = '81868';