Final answer:
The correct equation to calculate the change in profit with a change in sales and fixed expenses is not presented in the options. Profit change is found by considering changes in total revenue and variable costs, not fixed expenses which are constant.
Step-by-step explanation:
The correct equation to calculate the change in profit due to a change in sales and fixed expenses is none of the options provided. Profit is typically calculated as total revenue minus total costs. Total costs include fixed and variable costs. When looking to solve for the change in profit, variable costs and changes in sales volume need to be factored in, along with the consideration of the selling price per unit.
To calculate the change in profit, you would typically take the change in total revenue (which is the change in quantity sold multiplied by the selling price per unit) and subtract the change in total variable costs. Since fixed costs do not change with the volume of production, they would not vary with the change in sales directly. Therefore, none of the provided equations accurately represent how to calculate the change in profit based on changes in sales and fixed expenses. A more accurate formula might look like this:
Change in Profit = (Change in Sales x Selling Price per Unit) - (Change in Sales x Variable Cost per Unit)
It's important to note that these calculations assume that fixed expenses remain constant and the firm has already accounted for them in its initial profit calculations.