Answer
$\displaystyle \log_{3}[\frac{y^{4}}{x^{2}}]$
Work Step by Step
$4\log_{3}y-2\log_{3}x=\qquad \color{blue}{\text{ ...apply } \log_{a}x^{r}=r\log_{a}x}$
$=\displaystyle \log_{3}y^{4}-\log_{3}x^{2}=\qquad \color{blue}{\text{ ...apply } \log_{a}(\frac{x}{y})=\log_{a}x-\log_{a}y}$
$=\displaystyle \log_{3}[\frac{y^{4}}{x^{2}}]$
