How many annual interchanges in the millions occurred in 2011-12 when the number of annual entry/exits was 36.609 million?
create table table_18118221_1 (annual_interchanges__millions__2011_12 varchar, annual_entry_exit__millions__2011_12 varchar, PRIMARY KEY (annual_interchanges__millions__2011_12))
select annual_interchanges__millions__2011_12 from table_18118221_1 where annual_entry_exit__millions__2011_12 = "36.609"