If the interest rate on an account is 8.5% compounded yearly, approximately how many years will it take to triple the amount?

$3P = P(1 + 0.085)^{mt}$

$3 = 1.085^{1 ~ \cdot ~ t}$

$\ln 3 = \ln 1.085^t$

$\ln 3 = t \ln 1.085$

$t = \dfrac{\ln 3}{\ln 1.085}$

$t = 13.47 ~ \text{yrs}$