I want to know the whole process of calculation.

A mortgage for $200,000 with interest rate of 7.20%. fixed monthly payments, and term of 30 years was originated 10 years ago. If the loan's current balance is refinanced for the rest of the original term of at the rate of 6.30% with monthly payments, what is the implied annual savings rate given that the existing loan has a refinancing fee of 4% of the remaining balance at the time of refinancing? Assume the loan is not to be prepaid until the end of its term. Selected Answer: B. Between 6% and 8% Correct Answer: F. Between 14% and 16%