user: ### NOW ANSWER:
Question: What is the year when Kurtis Kraft 500F was the chassis?
Columns: ['Year', 'Entrant', 'Chassis', 'Engine', 'Points']
Types: ['real', 'text', 'text', 'text', 'real']
Sample row: [1950.0, 'Pat Clancy', 'Ewing', 'Offenhauser L4', 0.0]
SQL:

assistant: SELECT SUM("Year") FROM "Table" WHERE "Chassis" = 'Kurtis Kraft 500F';