There are 15 - 6 = <<15-6=9>>9 students who like French fries only.
There are 10 - 6 = <<10-6=4>>4 students who like burgers only.
So, 9 + 4 + 6 = <<9+4+6=19>>19 students like either French fries, burgers, or both.
Hence, 25 - 19 = <<25-19=6>>6 students do not like either fries or burgers.
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