Northern Star sells several products. Information of average revenue and costs is as follows: Selling price per unit $20.00 Variable costs per unit: Direct material $4.00 Direct manufacturing labor $1.60 Manufacturing overhead $0.40 Selling costs $2.00 Annual fixed costs $96,000 The company sells 12,000 units at the end of the year. 7) If direct labor and direct material costs increase by $1 each, contribution margin ________.