Answer
10.8 h
Work Step by Step
Recall: $\ln \frac{A_{t}}{A_{0}}=-\frac{0.693}{t_{1/2}}t$
$\implies \ln \frac{2.5\times10^{3}/s}{1.5\times10^{5}/s}=-\frac{0.693}{1.83\,h}\times t$
$\implies -4.09434456=-0.3786885\,h^{-1}\times t $
$\implies t= \frac{-4.09434456}{-0.3786885\,h^{-1}}$
$= 10.8\,h$
