Final answer:
The correct answer is option Contribution per unit of scarce resource.
Step-by-step explanation:
The concept most useful for solving production-planning problems involving multiple products and limited resources is contribution per unit of scarce resource. This method focuses on maximizing the use of limited resources by calculating the contribution margin, which is the revenue minus variable costs per unit, and then dividing this by the amount of the scarce resource that each unit of product uses.
This helps in determining which product or products should be prioritized in production to maximize overall profitability.