13.7 A pulpwood-forming machine was purchased and installed 8 years ago for $50,000. The declared sal vage value was $5000, with a useful life of 10 years. The machine can be replaced with a more efficient model that costs $90,000, including installa- tion. The old machine can be sold on the open market for $20,000. The cost to remove the old machine is $5000. Which are the relevant costs for the old machine