4. Confirm your calculations in Requirement 3 above by increasing the unit sales in your worksheet by 20% so that the Data area looks like this: A B 1 Chapter 5: Applying Excel 2 3 Data 4 Unit sales 72,000 units 5 Selling price per unit $ 10 per unit 6 Variable expenses per unit $ 7 per unit 7 Fixed expenses $ 171,000 (a) What is net operating income? (Negative amount should be indicated by a minus sign.) (b) By what percentage did the net operating income increase?