A family is considering installing a household solar energy system. The system has an installed cost of $1,250 and they reduce the homeowner's energy bill by $350 per year. The residual value of the solar panels is $500 at the end of their 5-year life. What is the annual effective IRR of this investment? Assume the family has a MARR of 10%. Please use the interpolation method and only fill in the number of your calculated result in the blank, e.g., if the result is 7.537%, fill in "7.54", also keep 2 digits after the decimal point