Your parents will retire in 19 years. They currently have $320,809, and they think they will need $1,799,335 at retirement. Assuming they don't save any additional funds, the annual interest rate they must earn to achieve their goal would be _%. (Round your answer to three decimal places. For example 1.23450 or 1.23463 will be rounded to 1.235 while 1.23448 will be rounded to 1.234)