The following is Arkadia Corporation's contribution format income statement for last month: Sales $1,500,000 Less: variable expenses 800,000 Contribution margin 700,000 Less: fixed expenses 300,000 Operating income $400,000 The company has no beginning or ending inventories and produced and sold 20,000 units during the month. Required: a) What is the company's contribution margin ratio? b) What is the company's break-even in units? c) If sales increase by 100 units, by how much should operating income i