Walsh Corporation produces and sells a single product. Data concerning that product appear below: Per Unit Percent of Sales Selling price $ 140 100 % Variable expenses 42 30 % Contribution margin $ 98 70 % Fixed expenses are $490,000 per month. The company is currently selling 6,000 units per month. The marketing manager would like to introduce sales commissions as an incentive for the sales staff. The marketing manager has proposed a commission of $11 per unit. In exchange, the sales staff would accept a decrease in their salaries of $58,000 per month. (This is the company's savings for the entire sales staff.) The marketing manager predicts that introducing this sales incentive would increase monthly sales by 100 units. What should be the overall effect on the company's monthly net operating income of this change? Select one: O a. increase of $588,700 O b. decrease of $115,300 c. increase of $700 d. increase of $56,900