how many routes are there?
select count(*) from routes
find the number of routes for each destination.
select count(*), dst_apid from routes group by dst_apid
what is the name and city of the destination airport that has the most routes ending there?
select t1.name, t1.city from airports as t1 join routes as t2 on t1.apid = t2.dst_apid group by t2.dst_apid order by count(*) desc limit 1