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 640 pounds. The tithes paid him 70 pounds per year for 31 years. What interest rate did the he rocelve on this investment? Note: Do not round intermediate calculations and enter your answer as a percent rounded to 2 decimal places, e.9. 32.16