What are the names of colleges with less than 13,000 students?
select cname from college where enr < 13000
Which of those are in AZ?
select cname from college where enr < 13000 and state = "AZ"
Combine that with colleges in LA that have more than 15,000 students?
select cname from college where enr < 13000 and state = "AZ" union select cname from college where enr > 15000 and state = "LA"