It was projected that a coal mine purchased 3 years ago for $7 million would hold 4,000,000 tons of coal. The volume of coal extracted has been 21,000, 18,000, and 20,000 tons, respectively, over the...

It was projected that a coal mine purchased 3 years ago for $7 million would hold 4,000,000 tons of coal. The volume of coal extracted has been 21,000, 18,000, and 20,000 tons, respectively, over the past 3 years. For the first year, the gross profits earned in those three years was $257,000, for the second year, $320,000, and for the third year, $340,000. Determine (a) each year's expense depletion allowance and (b) the percentage of the purchase price depleted to date.