Answer
$x=\displaystyle \frac{kz^{3}}{y}$
$y=\displaystyle \frac{kz^{3}}{x}$
Work Step by Step
$x$ varies directly as $z^{3}:\qquad x=kz^{3}$
$x$ varies inversely as $y :\displaystyle \qquad x=\frac{k}{y}$
Combined (jointly): $\displaystyle \qquad x=\frac{kz^{3}}{y}$
Solving for $y,$
multiply both sides by y (get it out of the denominator)
$xy=kz^{3}\qquad/\div x$
$y=\displaystyle \frac{kz^{3}}{x}$
