Required information [The following information applies to the questions displayed below.) Donaldson Company's contribution format income statement for the most recent month is shown below. Sales Variable expenses Contribution margin Fixed expenses Net operating income Total Per Unit $500,000 $12.50 300,000 7.50 200,000 $5.00 100,000 $20,000 The company sold 40,000 units in its most recent month and its relevant range of production is 30,000 to 50,000 units. Click here to download the Excel template, which you will use to answer the questions that follow Click here for a brief tutorial on Goal Seek in Excel. Click here for a brief tutorial on SOLVER in Excel, Click here for a a brief tutorial on Charts in Excel. Required: 1. In the Excel file: a. How is the contribution margin shown in cell B14 being calculated? b. How is the net operating income shown in cell B16 being calculated? c. How is the net profit margin percentage shown in cell 818 being calculated?