Zip-up Company provides the following data developed for its master budget: Sales price $11.00 per unit Costs: Direct materials $3.00 per unit Direct labor $4.75 per unit Variable overhead $0.50 per unit Factory depreciation $12,000 per month Supervision $13,000 per month Selling expense $0.25 per unit Administrative cost $9,000 per month Required: Prepare flexible budgets for sales of 18,000, 21,000 and 24,000 units. Use a contribution margin format