ANSWER:
The value of z is 4
STEP-BY-STEP EXPLANATION:
We have the following expression:
[tex]\frac{3}{z}=\frac{9}{12}[/tex]To know the value of z we must solve for z in the expression just like this:
[tex]\begin{gathered} 12\cdot3=9\cdot z \\ z=\frac{36}{9} \\ z=4 \end{gathered}[/tex]