DEPRECIATION: Company F purchased equipment for 150,000 on 1/1/2020. The equipment has a useful life of 5 years and a residual value of 30,000 and will produce 120,000 total units of production over the useful life. For 2020 the equipment had 30,000 units of production and for 2021 had 40,000 units of production. Using the units-of-production method of depreciation, what is the amount of depreciation expense for 2021?

a. 50,000

b. 40,000

c. 30,000

d. 24,000

e. None of the above