Final answer:
The total amount of interest paid on the mortgage would be $270,000.
Step-by-step explanation:
To calculate the total amount of interest paid on a mortgage, you can use the formula: Interest = Principal * Rate * Time. In this case, the principal is $100,000, the rate is 9%, and the time is 30 years.
So, the interest = $100,000 * 9% * 30 years = $270,000.
Therefore, the total amount of interest paid on a 30-year $100,000 mortgage at an interest rate of 9% would be $270,000.