Answer
$1.3\,\mu g$
Work Step by Step
$t=24\,h+9\,h= 33\,h$
$N_{0}=1.5\,\mu g$
$t_{1/2}=8\,days=8\times 24\,h=192\,h $
$k=\frac{0.693}{t_{1/2}}=\frac{0.693}{192\,h}=3.609375\times10^{-3}\,h^{-1}$
Recall: $\ln \frac{N_{t}}{N_{0}}=-kt$
$\implies \ln \frac{N_{t}}{1.5\,\mu g}=-3.609375\times10^{-3}\,h^{-1}\times33\,h=-0.11911$
$\implies \frac{N_{t}}{1.5\,\mu g}=e^{-0.11911}=0.88771$
$\implies N_{t}=1.5\,\mu g\times0.88771=1.3\,\mu g$
