Problem:
David's is saving for his retirement and as of today has accumulated the lump sum of $7348. David's goal is to retire at some time in the future (the unknown) with 9 times this amount.
Required:
Assuming that all of David's current retirement money is invested to earn an interest rate of 3.90%, how long, in years and in fractions of a year, will it take David to achieve his goal?
Please describe in detail and show all methods