help me on my home work pllz

if an amount of money is invested at an annual interest rate of 6%,it doubles every 12 years.if alejandra invests $500, how llong will it take her investment to exceed $2000 (assuming she doesn't contribute any additional funds)?

WEll it doubles every 12 years so    (assuming the initial statement is correct)

start                       $500

beginning of 12th year    $1000

beginnnig of 24th year    $2000

So 24 years. 

In 24 years, $500 would have grown to $2,024.47 @ 6% comp. annually. The formula you use is this: FV=PV(1 + R)^N, FV=Future value, PV=Present value, R=Interest rate per period, N=Number of periods.