Springer Products 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: Model X Model Y Model Z Selling price $55 $61 $78 Direct Materials $8 $8 $8 Direct Labor ($17 per hour) $17 $17 $34 Variable support cost ($9 per machine hour $9 $18 $18 Fixed support costs $13 $13 $13 Which model has the greatest contribution margin per machine-hour (and what is it)?