Which zip code had at least 100 trips taking place there?
select distinct zip_code from trip group by zip_code having count(*) >= 100
Give me the zip code where the average mean humidity is below 70
select zip_code from weather group by zip_code having avg(mean_humidity) < 70
Intersect those.
select zip_code from weather group by zip_code having avg(mean_humidity) < 70 intersect select zip_code from trip group by zip_code having count(*) >= 100