Untitled

select airports.name
	from routes, airports 
	where 
	airports.iata = routes.source and 
	source in (select
airports.iata
from airports 
where
country = 'United States' and 
	altitude - 500 > (select min(altitude)
from airports
where country = 'United States'))
	group by airports.name
	having count(routes.source) >= 2