The static budget, at the beginning of the month, for Jabari Company follows: Static budget: Sales volume: 2100 units; Sales price: $52.00 per unit Variable costs: $12.00 per unit; Fixed costs: $26,500 per month Operating income: $57,500 Actual results, at the end of the month, follows: Actual results: Sales volume: 1900 units; Sales price: $58.00 per unit Variable costs: $17.00 per unit; Fixed cost: $37,000 per month Operating income: $40,900 Calculate the sales volume variance for operating income