Oz Industries Ltd. sells several products. Information of average revenue and costs is as follows: Selling price per unit $23.00 Variable costs per unit: Direct material $4.00 Direct manufacturing labor $1.70 Manufacturing overhead $0.40 Selling costs $2.00 Annual fixed costs $100,000 The company sells 12,000 units at the end of the year. of direct labor and direct material costs increase by $1.00 each, contribution margin a. Increases by $12.000 b. decreases by $12,000 c. increases by $24,000 d. decreases by $24,000