Final answer:
To determine the new interest rate after the points purchase, subtract the number of points purchased from the original interest rate of 4.575%.
Step-by-step explanation:
To determine the new interest rate, we need to know the number of points purchased. Points are essentially fees paid upfront to reduce the interest rate on a loan. Let's say Brenna purchased n points. Each point typically costs 1% of the loan amount. So, if Brenna purchased n points, her new interest rate would be 4.575% - n%. For example, if Brenna purchased 0.5 points, her new interest rate would be 4.575% - 0.5% = 4.075%.