To determine how many kg does a 30-pound dog, considering that we know that 20 pounds are equal to 9 kg, you can use cross multiplication.
20pounds ____ 9kg
30pounds ____ xkg
The kg/pound proportion is the same for both rates so that:
[tex]\begin{gathered} \frac{9}{20}=\frac{x}{30} \\ 30(\frac{9}{20})=x \\ x=13.5 \end{gathered}[/tex]30 pounds are equal to 13.5kg.