Answer
(a). $t=63.01$
(b). $t=99.87$
Work Step by Step
$n(t)=n_0\times e^{rt}$. Whereas,$n(t)$ is population at time $t$, $n_0$ is Initial size of the population, $r$ is relative rate of growth, and $t$ is time.
(a). $n_0=7.1$, $r=0.011$
$n(t)=7.1e^{0.011t}=14.2$,
$e^{0.011t}=2$,
$0.011t=\ln2$,
$t=63.01$
(b). $n(t)=7.1e^{0.011t}=21.3$,
$e^{0.011t}=3$,
$0.011t=\ln 3$,
$t=99.87$
