Data for Hermann Corporation are shown below: Per Unit Percent of Sales Selling price $ 120 100% Variable expenses 78 65 Contribution margin $ 42 35% Fixed expenses are $84,000 per month and the company is selling 2,600 units per month. Required: 1-a. How much will net operating income increase (decrease) per month if the monthly advertising budget increases by $8,900, the monthly sales volume increases by 100 units, and the total monthly sales increase by $12,000?