On January 1, 2019, Rio Rio Co. purchased a machine for $39,980, and expects to use the machine a total of 32,000 hours over the next four years. Rio Co. set the salvage value on the machine at $3,500, and used the machine 6,000 hours in 2019 and 7,200 hours in 2020.

What is the amortization expense in 2020 if Rio Co. uses units-of-production amortization?

A) $6,840

B) $6,192

C) $8,208

D) $4,500

Please tell me how to solve above question. Thank you.