Answer
$\frac{4}{x^{2}}$
Work Step by Step
According to the negative exponent rule, $a^{-n}=\frac{1}{a^{n}}$.
Therefore, $4x^{-2}=\frac{4}{x^{2}}$.
Since there are no parentheses around $4x$, the base of the exponent is $x$ (and not $4x$).