Answer:
 Produce only Product B.
Step-by-step explanation:
The contribution margin per machine hour for product A is ...
 ($16 -$6)/(5 hour) = $2 per hour
The contribution margin per machine hour for product B is ...
 ($12 -$5)/(3 hour) ≈ $2.33 per hour
The company should produce the maximum possible number of the product that contributes the most per machine hour: Product B.