Answer
$a=3$.
Work Step by Step
$ 9x^{3}-15x\qquad$...find the GCF.
$9x^{3}=(3)\cdot 3\cdot(x)\cdot x\cdot x$
$-15x=-1\cdot(3)\cdot 5\cdot(x)$
GCF=$3x$
$9x^{3}-15x\qquad...$factor out the GCF
$=3x(3x^{2})-3x(5)\qquad...$apply the Distributive Property.
$=3x(3x^{2}-5)$
Comparing $3x $ with $ax$, we see that
$a=3$.
