Answer
$x(4-x)(16+4x+x^2)$
Work Step by Step
Factor out the greatest common factor, $x$, to obtain:
$=x(64-x^3)
\\=x(4^3-x^3)$
This binomial is a difference of two cubes.
RECALL:
$a^3-b^3=(a-b)(a^2+ab+b^2)$
Factor the difference of two cubes using the formula above with $a=4$ and $b=x$ to obtain:
$=x(4-x)(4^2+4(x) + x^2)
\\=x(4-x)(16+4x+x^2)$
