Given:
(y) varies directly as (z) and inversely as (x):
[tex]\begin{gathered} y\propto z;y\propto\frac{1}{x} \\ \\ so,y\propto\frac{z}{x} \end{gathered}[/tex]so, the equation will be:
[tex]y=\frac{kz}{x}[/tex]Where: k is the proportionality constant