i know that answer should come out to 273,614.28, but just not sure how to get that. i feel like i am messing something up with the 6.6% nominal interest rate. Again any help would be great.

A residential mortgage for 300,000 has monthly payments that are based on a 30-year payment period and a nominal interest rate of 6.6% convertible monthly. However, the mortgage agreement states that the borrower must repay the outstanding loan balance at the end of 7 years. What total amount will the borrower have to pay at the end of 7 years? Answer: 273,614.28