#### Answer

$3x(x-y)(x+y)(x^2+y^2)$

#### Work Step by Step

Factor out the greatest common factor, $3x$, to obtain:
$=3x(x^4-y^4)
\\=3x[(x^2)^2-(y^2)^2]$
The binomial is a difference of two squares.
RECALL:
$a^2-b^2=(a-b)(a+b)$
Factor the difference of two squares using the formula above with $a=x^2$ and $b=y^2$ to obtain:
$=3x(x^2-y^2)(x^2+y^2)$
The first binomial factor is a difference of two squares. Factor using the formula above with $a=x$ and $b=y$ to obtain:
$=3x(x-y)(x+y)(x^2+y^2)$