Answer
The half-life here is $0.173$ when $t=0$.
Work Step by Step
The exponential decay model is the following:
$Q(t)=Q_0∗e^{-t_s∗k}$
Where $t_s∗k=\ln2$, and $t_s$ is the half-life at $t=0$ and k is constant.
Here, $k=4$
$t_s∗k=ln2$
$t_s∗4=ln2$
$t_s=\frac{ln2}{4}=0.173$
Therefore the half-life here is $0.173$ when $t=0$.
