On 1/1/2015, Ahmad Company purchased equipment for $470,000 and estimated its useful life for 9 years with a residual value of $20,000 at the end of its life. On 1/1/2019 the company decided that the total estimated life should be 12 years with a residual value of $10,000 at the end of the estimated life. The depreciation expenses at the end of year 2019 on a straight-line basis will be: a. $30,000 O b. $32,500 O c. $31,250 d. $33,750