Gunpowder contains 75% nitre and 10% sulphur.

Let the amount of gunpowder that contains $9 \mathrm{~kg}$ nitre be $\mathrm{x} \mathrm{kg}$.

i.e., $\frac{75}{100} \times \mathrm{x}=9$

$\Rightarrow \frac{100}{75}=\frac{x}{9}$

$\Rightarrow x=\frac{900}{75}$

$\Rightarrow x=12$

$\therefore$ The amount of gunpowder containing $9 \mathrm{~kg}$ nitre is $12 \mathrm{~kg}$.

Let the amount of gunpowder containing $2.3 \mathrm{~kg}$ sulphur be $\mathrm{y} \mathrm{kg}$.

i.e., $\frac{10}{100} \times \mathrm{y}=2.3$

$\Rightarrow \frac{100}{10}=\frac{\mathrm{y}}{2.3}$

$\Rightarrow \mathrm{y}=\frac{230}{10}$

$\Rightarrow \mathrm{y}=23$

$\therefore$ The amount of gunpowder containing $2.3 \mathrm{~kg}$ sulphur is $23 \mathrm{~kg}$.