Selling price Variable expenses Contribution margin Percent of Per Unit Sales $ 90 63 100% 70 $ 27 30% Fixed expenses are $30,000 per month and the company is selling 2,000 units per month. Required: 1-a. How much will net operating income increase (decrease) per month if the monthly advertising budget increases by $5,000, the monthly sales volume increases by 100 units, and the total monthly sales increase by $9,000? 1-b. Should the advertising budget be increased?