Answer:
$22,317
Explanation:
Depletion unit method is used for mines, quarries and oil wells.
Depletion Expense = Depletion rate × Number of units taken in the period
Where,
Depletion rate = (Cost of Asset - Residual Value) ÷ Expected Total Contents in Units
            = ($531,197 - $46,043) ÷ 91,060 tons
            = $5.33 per unit
Therefore,
Depletion Expense = $5.33 × 4,187 tons
                = $22,317