What is the maximum capacity of each room?
select maxoccupancy from rooms
What is the number of people who actually stayed for each room reservation? The number of people include adults and kids.
select t1.adults + t1.kids from reservations as t1
How many times the number reached the maximum capacity?
select count(*) from reservations as t1 join rooms as t2 on t1.room = t2.roomid where t2.maxoccupancy = t1.adults + t1.kids;