If an individual will retire in 17 years and currently have $300,000, and will need $1 million at retirement. What annual interest rate must that person earn to reach the goal? Round your answer to two decimal places.

If money is deposited today in an account that pays 8.9% annual interest, how long will it take to double the money? Round the answer to the nearest whole number?

With Thanks

If you let P denote the present amount; E the ending amount; r the annual interest rate; n the number of years; and make a simplifying assumption (probably intended in these questions) that earnings compound annually, then the equation

E = P(1 + r)^n

solves both of your questions. In each of the two cases you're given 3 of the 4 variables, leaving you to solve for the fourth. In the first ques you're solving for r; in the second you're finding n.

Hint: In the second question you're not explicitly given any particular P or E, but that's irrelevant; just let E be 2 and P be 1, or any combo of values in which E is double the amount of P.

OK, that tees it up; now you step in to swat it out of the park.