human
Considering the provided database schema and associated query, produce SQL code to retrieve the answer to the query. 
###Database Schema: Rank, City 1, City 2, 2012 Passengers (in millions), 2011 Passengers (in millions), Distance
###Question: How many passengers (in millions) in 2011 flew through along the route that had 6.640 million passengers in 2012?
gpt
SELECT 2011 Passengers (in millions) FROM table WHERE 2012 Passengers (in millions) = 6.640