Question
Lee bought the same number of files and markers. The total cost of 4 files and 1 marker was $15. The total cost of 1 file and 4 markers was $30. He spent a total of $81. How many files did Lee buy?
4 m

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Lee bought the same number of files and markers. The total cost of 4 files and 1 marker was $15. The total cost of 1 file and 4 markers was $30. He spent a total of $81. How many files did Lee buy?