Final answer:
The break-even volume in units will not be impacted by the increase in the selling price and variable labor cost by the same amount, as the contribution margin per unit remains the same.
Step-by-step explanation:
The impact of increasing the selling price by $4 per unit, in response to an increase in variable labor costs by an identical amount, will have no impact on the break-even volume in units. This is because the increase in revenue per unit is exactly offset by the increase in costs per unit, keeping the contribution margin per unit unchanged.
Break-even analysis is centered around the concept that at the break-even point, total revenues are equal to total fixed and variable costs, resulting in zero profit. The break-even volume is found by dividing the total fixed costs by the contribution margin per unit, which is the selling price per unit minus the variable cost per unit. Since both the selling price per unit and the variable cost per unit have increased by the same amount, their difference, the contribution margin per unit, remains the same.
As a result, the original calculation of the break-even volume in units remains unchanged. Any shifts in either variable that do not affect their difference would not alter the break-even point. In this situation, since the increase in the selling price is directly proportional to the increase in variable costs, the break-even volume will not be impacted.