21. Data concerning Marchman Corporation's single product appear below. Percent of Unit Sales Selling price ............... $120 Variable costs ............ 72 60% Contribution margin... $48 40% The company is currently selling 4,000 units per month. Fixed expenses are $166,000 per month. The marketing manager believes that a $6,000 increase in the monthly advertising budget would result in a 130 unit increase in monthly sales. What effect will this increase have on the overall company's monthly net operating income? A. Decrease of $240 B. Decrease of $6,000 C. Increase of $240 D. Increase of $6,240