Initially invested $800 @ interest rate of 9%. How many years before the investment doubles?

to solve this problem, you need to use this formula:

A=P (1+r/n) n⋅t

A = total amount

P = principal or amount of money deposited,

r = annual interest rate

n = number of times compounded per year

t = time in years

but to save you time, it takes you 8 years and 16 days