How many female students (sex is F) live in BAL
select count ( * ) from student where sex = 'F' and city_code = 'BAL'
What are their last names?
select lname from student where sex = 'F' and city_code = 'BAL'
Can you also show me the last names of any male students (sex is M) who are below the age of 20?
select lname from student where sex = 'M' and age < 20