Answer:
Replacing the old machine would produce a net saving of $1,300
The sunk cost in this situation is the purchase cost (i.e $105,000) of the old machine.
Explanation:
Differential Analysis
Purchase cost of the new machine                 (83,000)
Savings from annual variable cost(8500×8)          68,000
Variable cost of running the new machine (5,000×8)  (40,000)
Scrap value of the old machine                     56,300 Â
Differential savings                               1,300 Â
Replacing the old machine would produce a net saving of $1,300
The sunk cost in this situation is the purchase cost (i.e $105,000) of the old machine. It is a past cost incurred as a result old decision.