Answer
(a). $T(t)=60+38.6e^{-0.1947t}$
(b).$t=5.99$ hour ago
Work Step by Step
$T(t)=T_s+D_0e^{-kt}$. Whereas, $T(t)$ is a temperature at a time $t$, $T_s$ is the surrounding temperature, $D_0$ is the Initial temperature difference between the object and it's surrounding, $k$ is a positive constant that depends on the type of object.
$k=0.1947$, $T_s=60$, $T_0=98.6$, $D_0=98.6-60=38.6$,
(a). $T(t)=60+38.6e^{-0.1947t}$
(b). $72-60=38.6e^{-0.1947t}$,
$0.311=e^{-0.1947t}$,
$\ln 0.311=-0.1947t$,
$t=5.99$ hour ago
