On January 1, 2019, 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 straight-line amortization?

A) $6,875

B) $9,120

C) $12,000

D) $18,240

I have no idea how to calculate. Please tell me how to do. Thank you.