Answer
$\frac{1}{y^{4}}$
Work Step by Step
We know that $a^{−n}=\frac{1}{a^{n}}$ and $\frac{1}{a^{-n}}=a^{n}$ (as long as a is a nonzero real number and n is an integer).
Therefore, $\frac{(y^{4})^{2}}{y^{12}}=\frac{y^{4\times2}}{y^{12}}=\frac{y^{8}}{y^{12}}=y^{8-12}=y^{-4}=\frac{1}{y^{4}}$.