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TB Nelson Company prepares monthly financial statements and uses the gross profit method to estimate ending inventories. Historically, the company has had a 40% gross profit rate. During June, net sales amounted to $180,000; the beginning inventory on June 1 was $54,000; and the cost of goods purchased during June amounted to $90,000. The estimated cost of TB Nelson Company's inventory on June 30 is: A) $21,600. B) $36,000. C) $72,000. D) $126,000