80% 4. Emma Corporation produces and sells a single product. Data concerning that product appear below: Per Unit Percent of Sales Selling price S150 100% Variable expenses 30 20 Contribution margin $120 The company is currently selling 7,000 units per month. Fixed expenses are $615,000 per month. The marketing manager believes that a $21,000 increase in the monthly advertising budget would result in a 180 unit increase in monthly sales. What should be the overall effect on the company's monthly net operating income of this change? A. increase of $600 B. decrease of $600 C. decrease of $21.000 D. increase of $21,600