A homeowner took out a $20-$year fixed$-$rate mortgage of $$75,000.$ The mortgage was taken out $12$ years ago at a rate of $7\mathrm{.}5$ percent. If the homeowner refinances, the charges will be $$1,550.$ What is the highest interest rate at which it would be beneficial to refinance the mortgage? APR $\%?$

Note: Do not round intermediate calculations. Enter your answer as a percent rounded to $2$ decimal places.