(Can you please explain to me how you got the answer)

In a given department, the beginning inventory of 8,000 units was 60% complete as to materials, labor and overhead. A total of 9,000 units were started and completed during the period, and the ending inventory of 10,000 units was 40% complete as to materials, labor and overhead. The equivalent production for the period in units are:

a)18,200

b) 16,200

c) 12,200

d) 17,800