Answer
$-8x^4$
Work Step by Step
Let $x$ be the missing factor:
$x(-\frac{1}{4}xy^3)=2x^5y^3$
Multiply both sides of the equation by $\left(-\frac{4}{xy^3}\right)$:
$x(-\frac{1}{4}xy^3)\left(-\frac{4}{xy^3}\right)=2x^5y^3\left(-\frac{4}{xy^3}\right)$
Simplify each side:
$x=(2\cdot (-4))x^{5-1}y^{3-3}$
$x=-8x^4$
The missing factor is $-8x^4$.
