At the end of 2020, Blackfly Ltd. estimated an annual depreciation expense of $6,000 for its truck using the straight-line method. The income tax rate is 10%. The expected life of the truck was 4 years, with no residual value. The original cost of the truck was likely Select one: O a $24,000 O b. $20,000 O c. $ 6,000 O d. $ 30,000