Sunk Cost Definition
A sunk cost is a cost that an entity has incurred, and which it can no longer recover.
Sunk or Stranded Cost
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True stranded costs are the fair market value of a firm’s assets minus their historical, depreciated book value. If the book value is greater than the fair market value, then the firm has stranded costs. If the fair market value is greater than book value, then the firm has no stranded costs.
In the context of the article the firm level stranded costs are the same as sunk costs except the costs are called "stranded" when the cause of the change in market value is driven by changes in public regulations.
Context of Question
Market value of firm assets minus depreciated book value equals sunk cost:
150,000 - 300,000 = -150,000
One could also state the sunk cost as a positive value however it represents a loss that cannot be recovered compared to the depreciated book value of assets.