The correct answer is $\boxed{\text{B. }8.5\%}$.
The operating ratio is a measure of a company’s profitability. It is calculated by dividing a company’s operating expenses by its revenue. A lower operating ratio indicates that a company is more profitable, as it is spending less money on its operations relative to its revenue.
The operating profit ratio is a measure of a company’s profitability. It is calculated by dividing a company’s operating profit by its revenue. A higher operating profit ratio indicates that a company is more profitable, as it is generating more profit from its operations relative to its revenue.
To calculate the operating profit ratio, we first need to calculate the operating profit. The operating profit is calculated by subtracting the operating expenses from the revenue. In this case, the operating expenses are $91.5 million and the revenue is $100 million. Therefore, the operating profit is $8.5 million.
Now that we know the operating profit, we can calculate the operating profit ratio. The operating profit ratio is calculated by dividing the operating profit by the revenue. In this case, the operating profit ratio is $8.5 million / $100 million = 8.5%.
Therefore, the correct answer is $\boxed{\text{B. }8.5\%}$.