Question 1105250
Possible roots based on Rational Roots Theorem include -3, +3, -5, +5, and others.
Trying polynomial, OR synthetic division gives this factorization for f:
{{{f(x)=(x-5)(x+3)^2}}}


Since the description gives that the box has a square base, the side of each base dimension is the {{{x+3}}}.  Length is {{{x-3}}} and width is {{{x-3}}}.


The height of the box would be {{{x-5}}}.