user: Question: How many different total number of transit passengers are there in London Luton?
Columns: ['Rank', 'Airport', 'Total Passengers', '% Change 2007/2008', 'International Passengers', 'Domestic Passengers', 'Transit Passengers', 'Aircraft Movements', 'Freight ( Metric Tonnes )']
Types: ['real', 'text', 'real', 'text', 'real', 'real', 'real', 'real', 'real']
Sample row: [1.0, 'London Heathrow', 67054745.0, '1.5%', 61344438.0, 5562516.0, 147791.0, 478693.0, 1397054.0]
SQL:

assistant: SELECT "Transit Passengers" FROM "Table" WHERE "Airport" = 'London Luton';