If fixed costs are $450,000, the unit selling price is $75, and the unit variable costs are $50, the old and new break-even sales (units), respectively, if the unit selling price increases by $10 are a.18,000 units and 12,857 units b.6,000 units and 5,294 units c.18,000 units and 6,000 units d.9,000 units and 15,000 units