Stoney Hollow Middle School is taking a field trip to the zoo. There are 109 fifth graders, 115 sixth graders, and 118 seventh graders. There are 4 teachers and 2 parents from each grade coming along to chaperone on the trip. There are 72 seats on each school bus. How many buses are needed for the field trip?
Please reason step by step, and put your final answer within \boxed{}.
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