Answer
$-16x+36x^3$
Work Step by Step
Using $(a-b)(a+b)=a^2-b^2$, or the product of the sum and difference of like terms, the given expression, $
-4x(2-3x)(2+3x)
,$ is equivalent to
\begin{array}{l}\require{cancel}
-4x[(2)^2-(3x)^2]
\\\\=
-4x(4-9x^2)
.\end{array}
Using the Distributive Property, the expression, $
-4x(4-9x^2)
,$ is equivalent to
\begin{array}{l}\require{cancel}
-16x+36x^3
.\end{array}