The static budget, at the beginning of the month, for Helloise Dcor Company follows: Static budget: Sales volume: 2,100 units: Sales price: $58.00 per unit Variable cost: $14.00 per unit: Fixed costs: $27,000 per month Operating income: $65,400 Actual results, at the end of the month, follows: Actual results: Sales volume: 1,850 units: Sales price: $59.00 per unit Variable cost: $18.00 per unit:Fixed costs $35,000 per month Operating income: $40,850 Calculate the sales volume variance for variable costs.