AbeCo, a luggage manufacturing company, borrowed $75,000 from the bank to purchase a machine that was estimated to produce 120,000 suitcases; its expected residual value is $15,000. During 2017 and 2018, the machine produced 20,000 and 28,000 units, respectively. Calculate depreciation for 2017 and 2018 assuming the units-of-production method is used:

a. To the nearest whole month 

b. Using the half-year convention