Listed here are three separate series of costs measured at various volume levels. Volume (Units) 0 260 Series 1 $ 200 Series 2 $ 0 Series 3 $ 500 200 2,340 500 520 200 4,680 500 780 400 7,020 500 1,040 800 9,360 500 1,300 600 11,700 500 1,560 600 14,0 ,040 500 Examine each series and identify whether it is best described as a fixed, variable, or step-wise cost. Hint: It can help to graph each cost series. Series 1 Series 2 Series 3