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 $800$ pounds. The tithes paid him $78$ pounds per year for $30$ 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$.,32\mathrm{.}16.$

Interest rate