Answer
$\frac{1}{y^{4}}$
Work Step by Step
According to the quotient rule for exponents, $\frac{a^{m}}{a^{n}}=a^{m-n}$.
Therefore, $\frac{y^{8}}{y^{12}}=y^{8-12}=y^{-4}$.
According to the negative exponent rule, $a^{-n}=\frac{1}{a^{n}}$.
Therefore, $y^{-4}=\frac{1}{y^{4}}$.