An investor was afraid that he would become like King Lear in his retirement and beg hospitality from his children, so he purchased grain "tithes," or shares in farm output, for 660 pounds. The tithes paid him 71 pounds per year for 32 years. What interest rate did the he receive on this investment? Note: Do not round intermediate calculations and enter your answer as a percent rounded to 2 decimal places, e.g., 32.16. Interest rate %