Spartan systems reported total sales of $300,000, at a price of $20 and per unit variable expenses of $12, for the sales of their single product. total per unit sales $300,000 $20 variable expenses 180,000 12 contribution margin 120,000 $8 fixed expenses 100,000 net operating income $20,000 what is the amount of contribution margin if sales volume increases by 30%? $19,500 $15,000 $156,000 $120,000