user: Question: On how many dates did the Michigan International Speedway hold a round?
Columns: ['Rnd', 'Race Name', 'Circuit', 'City/Location', 'Date', 'Pole position', 'Fastest lap', 'Winning driver', 'Winning team', 'Report']
Types: ['text', 'text', 'text', 'text', 'text', 'text', 'text', 'text', 'text', 'text']
Sample row: ['1', 'Dailkyo IndyCar Grand Prix', 'Surfers Paradise Street Circuit', 'Surfers Paradise , Australia', 'March 22', 'Al Unser, Jr.', 'Emerson Fittipaldi', 'Emerson Fittipaldi', 'Marlboro Team Penske', 'Report']
SQL:

assistant: SELECT COUNT("Date") FROM "Table" WHERE "Circuit" = 'Michigan International Speedway';