Following are four series of costs measured at various volume levels. Identify each series as either fixed, variable, mixed, or step-wise. Hint. It can help to graph each cost series. Volume (Units) Series A Series B Series C Series D 0 400 $ 2,780 $ 1,280 $ 5,280 $ 0 3,380 1,280 5,280 3,880 800 3,980 2,560 5,280 7,760 1,200 4,580 2,560 5,280 11,640 1,600 5,180 3,840 5,280 15,520 2,000 5,780 3,840 5,280 19,400 2,400 6,380 5,120 5,280 23,280 Series A Series B Series C Series D