Answer
$6.3$ months
Work Step by Step
If $y=A(1.19)^{t}, \qquad$(by part a.)
we want to find t for which $y=3A$.
$3A=A(1.19)^{t} \qquad/\div A$
$3=(1.19)^{t} \qquad/\log(...)$
$\log 3=t\log 1.19$
$t=\displaystyle \frac{\log 3}{\log 1.19}\approx 6.3$ months.
