To describe the accountant's fee structure, we need to account for both the flat fee and the hourly rate.
- The accountant charges a flat fee of $150.
- In addition to this flat fee, there is a charge of $25 for each hour worked on completing the taxes.
Let \( x \) be the number of hours worked, and \( y \) be the total fee charged.
The total fee can be expressed with the following equation: \[ y = 150 + 25x \]
This equation indicates that the total fee \( y \) is equal to the initial flat fee of $150 plus $25 multiplied by the number of hours \( x \) worked.
So, the correct answer is: \( y = 150 + 25x \).