How do I determine what the book value for an asset, so that I know the minimum price to charge bidders?

Product A

Purchase Price: 2,500,000

Salvage Value: 200,000

Useful Life: 14 years

Age: 2 years

Product B

Purchase Price: 5,000,000

Salvage Value: 750,00

Useful Life: 10 years

Age: New

Is it based on the assets age - for example, for Product A, you'd subtract 2 x $164,286 from the purchase price to get the book value.