Answer
The volume of the package in terms of the length of a side of its square front $x$ is, $V=108{{x}^{2}}-4{{x}^{3}}\text{ cubic inches}$.
Work Step by Step
Consider the length plus girth of provided package: $\text{108 inches}$
Now, the measurement of the length plus girth is the sum of the distance around that package and the longest side of girth
$4x+y=108$
Or
$y=10-8-4x$
The volume of provided package, $V=l\cdot w\cdot h$
Substitute $y$ for $l$ , and $x$ for $w$ and $h$ in the above equation
$\begin{align}
& V=y\cdot x\cdot x \\
& =y\cdot {{x}^{2}}
\end{align}$
Substitute $108-4x$ for $y$ in the above equation
$V=\left( 108-4x \right)\cdot {{x}^{2}}$
Or
$V=108{{x}^{2}}-4{{x}^{3}}$
The required volume of the package in terms of the length of a side of its square front $x$ is, $V=108{{x}^{2}}-4{{x}^{3}}\text{ cubic inches}$.
