Answer
$ t\approx 7.9$ minutes
Work Step by Step
Graphing, the solution is at $ t\approx 7.9$ minutes.
(see below)
Algebraically, $ 70=145e^{-0.092t}\qquad $ ... $/\div 145$
$\displaystyle \frac{70}{145}=e^{-0.092t}\qquad $... $/\ln(...)$
$\displaystyle \ln(\frac{70}{145})=-0.092t\qquad $... $/\div(-0.092)$
$ t=\displaystyle \frac{\ln(70/145)}{-0.092}\approx 7.915635873$
$ t\approx 7.9$ minutes
