Per Unit Percent of Sales Selling price $170 100% Variable expenses $85 50% Contribution margin $85 50% The company is currently selling 6,600 units per month. Fixed expenses are $505,600 per month. The marketing manager believes that a $6,400 increase in the monthly advertising budget would result in a 160 unit increase in monthly sales. What should be the overall effect on the company's monthly net operating income of this change would be closest to a.