Final answer:
A 10% increase in fixed costs along with a 10% decrease in sales leads to a decrease in net profit, but the exact amount can't be determined without more information about the cost and sales figures, as well as the company's cost structure.
Step-by-step explanation:
When considering the impact of a 10% increase in fixed costs along with a 10% decrease in sales, the effect on net profit cannot be determined without additional information. This is because the actual dollar amount of the cost increase and the sales decrease would need to be known to calculate the effect on net profit. Furthermore, the relationship between costs, sales, and profits can vary depending on the business structure, the industry, and the specific financial circumstances of a company.
It is also important to note that a decrease in sales does not always translate directly into an equivalent percentage decrease in net profit. The interplay of all costs, including variable costs and the structure of fixed costs, will determine the overall impact on profitability. As such, the correct choice is c) A decrease in net profit, but we don't have enough information to determine the amount.