Answer
The required equation is $x=kz\left( y-w \right)$ and the value of $y$ is $\frac{x+kzw}{kz}$.
Work Step by Step
As the value of $x$ varies directly as $z$ and $\left( y-w \right)$ , we have
$x=kz\left( y-w \right)$
Where $k$ is a constant.
Now, solve the above equation for $y$.
$\begin{align}
& x=kz\left( y-w \right) \\
& x=kzy-kzw \\
& kzy=x+kzw \\
& y=\frac{x+kzw}{kz}
\end{align}$
