13. Oslo Company prepared the following contribution format income statement based on a sales volume of 1,000 units (the relevant range of production is 500 units to 1,500 units): Sales Variable expenses $24,800 13,600 Contribution margin Fixed expenses 11,200 7,728 Net operating income $ 3,472 Required Using the degree of operating leverage, what is the estimated percent increase in net operating income ofa 4% increase in sales? (Do not round intermediate calculations. Round your answer to 2 decimal places.) Percent increase in net operating income