Mark Corporation produces two models of calculators. The Business model sells for $60, and the Math model sells for $30. The variable expenses are given below: Business Model Math Model Variable production costs per unit $20 $21 Variable selling and administrative expenses per unit $ 10 $ 7 The fixed expenses are $85,000 per month. The expected monthly sales of each model are: Business, 2,000 units; Math, 1,500 units. The contribution margin ratio for the Business model is: (Do not round intermediate calculations.) 30% 50% ?? 70% 80%