user: Question: What Engine has a Finish of 21?
Columns: ['Year', 'Chassis', 'Engine', 'Start', 'Finish', 'Entrant']
Types: ['real', 'text', 'text', 'text', 'text', 'text']
Sample row: [1977.0, 'Parnelli VPJ6B', 'Cosworth', '7', '20', 'Interscope Racing']
SQL:

assistant: SELECT "Engine" FROM "Table" WHERE "Finish" = '21';