You are in need of cash and turn to your uncle, who has offered to lend you some money. You decide to borrow $$1,390$ and agree to pay back $$1,580$ in two years.

Problem $5\mathrm{.}15($a$1)$

What annual interest rate is your uncle charging you? $($Round intermediate calculations to $4$ decimal places, e$.$g$.2\mathrm{.}1525$ and final answer to $2$ decimal places, e$.$g$.8\mathrm{.}72.)$

Rate of interest charged by uncle $\%$