A machine with a cost of HK$400,000 has an estimated residual value of HK$25,000 and an estimated useful life of 5 years or 15,000 hours. It is to be depreciated using the units-of-activity method of depreciation. What is the amount of depreciation for the second full year, during which the machine was used 5,000 hours?

a. HK$125,000

b. HK$75,000

c. HK$108,333

d. HK$133,333