Find the average cost per item when the required number of item is produced.
C(x) = 8.5x + 10,400
Find cost for 200 items.
C(200) = 8.5(200) + 10,400
= 1,700 + 10,400
= 12,100 = total cost of 200 items
12100/200 = avg cost per item for 200 items = 60.5