Answer
$a^8$; Alice moved $a^{-3}$ to the numerator, but she subtracted it instead of adding it to $a^5$.
Work Step by Step
Alice moved $a^{-3}$ to the numerator, but she subtracted it instead of adding it to $a^5$. When moving negative exponents to the numerator, you must make them positive.
$\frac{a^5}{a^{-3}}$
$a^8$