Donovan Company incurred the following costs while producing 500 units: direct materials, $10 per unit; direct labor, $25 per unit; variable manufacturing overhead, $15 per unit; total fixed overhead costs, $10,000; variable selling and administrative costs, $5 per unit; total fixed selling and administrative costs, $7,500. There are no beginning inventories. What is the operating income using variable costing if 450 units are sold for $100 each