Braun's Brakes manufactures three different product lines, Model X, Model Y, and Model Z. Considerable market demand exists for all models. The following per unit data apply: Selling price direct materials direct labor Model X Model Y Model Z 64 60 70 7 6 12 122 12 13 4 8 24 24 8 fixed support costs 10 10 10 10 What is the contribution margin per machine hour of the product that should be produced when there is a limited number of machine hours available? ($12/labor hour) variable support costs ($4/ machine hour)