Answer
$-x(x-7)(x+6)$
Work Step by Step
Factoring the negative $GCF=
-x
,$ the given expression is equivalent to
\begin{array}{l}\require{cancel}
-x^3+x^2+42x
\\\\=
-x(x^2-x-42)
.\end{array}
Using the factoring of trinomials in the form $x^2+bx+c,$ the $\text{
expression
}$
\begin{array}{l}\require{cancel}
-x(x^2-x-42)
\end{array} has $c=
-42
$ and $b=
-1
.$
The two numbers with a product of $c$ and a sum of $b$ are $\left\{
-7,6
\right\}.$ Using these two numbers, the $\text{
expression
}$ above is equivalent to
\begin{array}{l}\require{cancel}
-x(x-7)(x+6)
.\end{array}