Answer
$$z=\frac{192}{y}$$
Work Step by Step
According to the information given, we can write the following relation:
$z=\frac{k}{y}$
To find the equation, we have to find the constant of proportionality ($k$).
If $z=12$ and $y=16$
$12=\frac{k}{16}$
$k=12\times 16$
$k=192$
$z=\frac{192}{y}$