Shipping charges at an online bookstore are $4 for one book, $6 for two books, and $7 for three to five books. Last week, there were 6400 orders of five or fewer books, and total shipping charges for these orders were $33,600. The number of shipments with $7 charges was 1000 less than the number with $6 charges. How many shipments were made in each category (one book, two books, three-to-five book?

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