Lucy has a machine valued at $100,000 and accumlated amortization of $20,000 on his Decemeber 31, 2019 Balance sheet. The useful life of the machine is 10 years. What is the net book value of the machine on December 31, 2020.

a) $100,000

b) $80,000

c) $70,000

d) $10,000

e) none of the above is correct