A certain store found that last year the average (arithmetic mean) monthly sales from January through October was $120,000. In November and December, the monthly sales were 3 and 5 times, respectively, the average for the other 10 months. What was the store's average monthly sales last year?
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A $180,000
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B $216,000
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C $252,000
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D $318,000
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E$360,000