I'll use my own formula (similar to yours tho)
A=future amount
p=invested
r=rate in decimal
n=number of times per year compounded
t=time in years
so
when will A=2P
subsitute 2P for A
also quarterly means 4 times a year or n=4
and 12%=0.12=r
so
divide both sides by P
simplify
take the ln of both sides
divide both sides by 4ln(1.03)
use calculator
5.86244=t
about 5.9 years
A=future amount
p=invested
r=rate in decimal
n=number of times per year compounded
t=time in years
so
when will A=2P
subsitute 2P for A
also quarterly means 4 times a year or n=4
and 12%=0.12=r
so
divide both sides by P
simplify
take the ln of both sides
divide both sides by 4ln(1.03)
use calculator
5.86244=t
about 5.9 years