Finding the required interest rate: Your parents will retire in 19 years. They currently have $350,000 saved; they think they will need $800,000 at retirement. What annual interest rate must they earn...

Finding the required interest rate: Your parents will retire in 19 years. They currently have $350,000 saved; they think they will need $800,000 at retirement. What annual interest rate must they earn to reach their goal, assuming they don’t save any additional funds?