log (p^-6/q^-2) =
??
& log p^3/log q^7
What are your expressions for x and y? You didn't provide them so we don't know what we're supposed to replace p and q with.
Also:
$\displaystyle \frac{\log p^{3}}{\log q^{7}}\: {\color{red} \neq}\: \log \left(p^{3}q^{7}\right)^{\frac{1}{2}}$
Not sure how you made that step.