Listed here are four series of separate costs measured at various volume levels. Volume Series 1 Series 2 Series 3 Series 4 (Units) $ 5,000 $5,000 $ 6, 000 $ 500 5,000 5, 000 18, 500 15,000 1, 000 5,000 5,000 31,000 30,000 1, 500 10,000 5,000 43, 500 45,000 2,000 10,000 5, 000 56, 000 60, 000 2, 500 15,000 5,000 68, 500 75,000 3, 000 15,000 5,000 81,000 90,000 Examine each series and Identify whether it is best described as a fixed, variable, step-wise, or curvilinear cost. It can help to graph the cost series. Series 1 Series 2 Series 3 Series 4