A sample contains $10^{-2} \mathrm{~kg}$ each of two substances $A$ and $B$ with half lives 4 s and 8 s respectively. The ratio of then atomic weights is $1: 2$. The ratio of the amounts of $A$ and $B$ after $16 s$ is $\frac{x}{100}$. the value of $x$ is
$\_\_\_\_$ .
