If $7000 is placed in account with an annual interest of 5.5% how long will it take the amount to double if the interest is compounded annually?

A=future amount
P=present amount
r=rate in decimal
n=number of times per year compounded
t=time in years

how many years to double
basically
A=2P at t=?
so we can simplify and ignore the pricipal given and do

r=5.5%=0.055
n=1
t=t




take the ln of both sides

divide both sides by ln1.055

use calculator to aproximate
12.9462=t
about 12.9 years