I want to know the whole process of calculation.

An existing mortgage has interest rate of 7.20%. fixed monthly payments, remaining term of 22 years, and current balance of $160,600. If the loan's balance is refinanced for 22 years 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: A. Below 13% Correct Answer: D. Between 15% and 16%