Answer:
Sunk cost = WDV of old machinery costing $431,000 - Any amount recovered.
Explanation:
Sunk cost is the cost that has actually been incurred and can not be avoided in any manner, currently while making both the decisions whether to buy model 220 machine or 370 machine we incurred the cost of dropping the old machinery of value of $431,000.
Therefore the book value of old machinery costing $431,000 is the sunk cost incurred in making the decision of buying new model.
In case any amount is recovered from sale of such amount then such amount recovered shall be deducted from the Written down value (WDV) of the old machinery and that will be our sunk cost.
Sunk cost = WDV of old machinery costing $431,000 - Any amount recovered.