Listed here are four series of separate costs measured at various volume levels.

Volume (Units)			Series 1			Series 2			Series 3			Series 4
	0		$	0		$	450		$	800		$	100
	100			800			450			800			105
	200			1,600			450			800			120
	300			2,400			450			1,600			145
	400			3,200			450			1,600			190
	500			4,000			450			2,400			250
	600			4,800			450			2,400			320

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