Equipment with a cost of $500,000 has an estimated salvage value of $100,000 and an estimated life of 8 years or 20,000 hours. It is to be depreciated using the units-of-activity method. What is the amount of depreciation for the first full year, during which the equipment was used 4500 hours? $90,000 O a. $80,000 O. $50,000 . $82,500 d