Answer:
1. Depletion for 2021 will be derived if the "tons which were extracted and sold immediately" is divided by "the Depletion per ton"
Depletion for 2021 = Extracted and sold tons in 2021 / depletion per ton
Depletion for 2021 = 249,000 tons * $5 per tons
Depletion for 2021 = $1,245,000
Where as the depletion per ton is be derived when the purchase price plus additional costs necessary is divided extract of tons of coals during the 4 year period.
Depletion per ton = $4,950,000 / 990000
Depletion per ton = $5 per ton
2. Depletion is not considered as part of product cost. It is shown as expense on income statement and reduced from the value of natural resource. So it is equivalent to depreciation of assets.