331 students went on a field trip. 6 buses were filled and 7 students traveled in cars. how many students were in each bus?

Total number of students = 331
total students that travelled in car = 7
total students that travelled in bus = 331 - 7
                                                      = 324
total number of buses = 6
Now, 
Total number of students in each bus = total students travelling in bus / total bus
                                                            = 324 / 6
                                                            = 54 students

So, there were 54 students in each bus.

331--7=324 student in 6 budes each bus will have 324/6 = 54 student in each bus.