Listed here are three separate series of costs measured at various volume levels. Volume (Units). Series 1 0 200 $ 800 Series 2 $0 Series 3 $500 800 1,000 500 400 800 3,600 500 600 1,600 5,400 500 800 3,200 7,200 500 1,000 1,200 2,400 9.000 500 2,400 10,000 500 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