The average (arithmetic mean) cost per book for the 12 books on a certain table is k dollars. If a book that costs 18 dollars is removed from the table and replaced by a book that costs 42 dollars, then in terms of k, what will be the average cost per book, in dollars, for the books on the table?
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Ak + 2
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Bk - 2
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C$${12}+\frac{24}{k}$$
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D$${12}-\frac{24}{k}$$
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E12k - 6
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正确答案: A