A histogram titled, guests in each hostel room, plots number of hostel rooms, versus number of guests, from 0 to 23, in increments of 3. bar heights are approximately as follows. from 0 to 3, 3. from 4 to 7, 5. from 8 to 11, 8. from 12 to 15, 6. from 16 to 19, 2. from 20 to 23, 1.
how many hostel rooms are there?