Bret takes a 9 hour train ride to go to Boston.   He spends 2 hours reading a book, 1 hour to eat his dinner, and 3 hours watching movies on his computer.  How many hours does he have left to take a nap?
For all his activities on the train, Bret spends 2 + 1 + 3 = <<2+1+3=6>>6 hours.
For his nap, he has 9 - 6 = <<9-6=3>>3 hours left.
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