Raleigh, North Carolina:

Raleigh-Durham International Airport, the region's primary airport and the second-largest in North Carolina, located northwest of downtown Raleigh via Interstate-40 between Raleigh and Durham, serves the city and greater Research Triangle metropolitan region, as well as much of eastern North Carolina. The airport offers service to more than 35 domestic and international destinations and serves approximately 10 million passengers a year. The airport also offers facilities for cargo and general aviation. The airport authority tripled the size of its Terminal 2 (formerly Terminal C) in January 2011.

Please answer a question about this article. If the question is unanswerable, say "unanswerable".  What are there 20 million of each year at the airport?
unanswerable