What are the names of colleges where students tried for the goalie position?
select cname from tryout where ppos = 'goalie'
Of those, which also had students that tried out for the mid position?
select cname from tryout where ppos = 'goalie' intersect select cname from tryout where ppos = 'mid'
How many of them are there?
select count(*) from (select cname from tryout where ppos = 'goalie' intersect select cname from tryout where ppos = 'mid')