The fifth-grade classes at brookfield school used five identical buses to go on a field trip. •there were a total of 40 seats on each bus. •all of the seats on four buses were filled. •the fifth bus had 4/5 of the seats filled. •1/8 of all the passengers on the buses were adults. how many adults went on the field trip.

For the first 4 buses divide 40 by 8 to get the number of adults for those buses, it should be five.
For the bus with 4/5 of the seats filled you'll first need to find out how many seats 4/5 of the bus would amount to.  To do this multiply 40 by 4/5, you should get 32.  Then you divide 32 by 8 and you'll get 4.
The adults on the 5 buses would be 5 + 5 + 5 + 5 + 4 = 24.