单选题 89. The following data are for Sponge Corporation: Flexible Budget for Master Actual Sales Actual Budget Activity Units 18,000 16,000 18,000 Sales $360,000 $320,000 $360,000 Variable costs 234,000 192,000 216,000 Contribution margin $126,000 $128,000 $144,000 Fixed costs 76,000 80,000 80,000 Operating income $50,000 $48,000 $64,000 The total of the sales-activity variances is