Asum of money invested will double after 6 years. if the interest is compounded quarterly, what is the rate?

We'll say principal = 100 and total = 200
a)  exp = log(total / principal) / (n* years)
where "n" is the number of compounding periods per year
exp = log (200 / 100) / (4*6)
exp = log (2) / (24)
exp = 0.30102999566 / 24
exp = 0.0125429165

b) rate = (10^exp -1) * n
rate = (10^0.0125429165 -1) * n
rate = (1.0293022367 -1) * n
rate = .0293022367 * 4
rate = 0.1172089468
rate = 11.72089468  %

See?  It's just that simple.  LOL