Plaza Corporation observed that when 25,000 units were sold, a particular cost amounted to $70,000, or $2.80 per unit. When volume increased by 15%, the cost totaled $80,500 (i.e., $2.80 per unit). The cost that Plaza is studying can best be described as a:

		variable cost.
		fixed cost.
		semivariable cost.
		discretionary fixed cost.
		step-fixed cost.