What are the markets with at least 30 shops?
select * from market where num_of_shops > 30
50 shops?
select * from market where num_of_shops > 50
What are their phones?
select t3.name from phone_market as t1 join market as t2 on t1.market_id = t2.market_id join phone as t3 on t1.phone_id = t3.phone_id where t2.num_of_shops > 50