smc

We are given: $$\frac{b^2}{ac}=x^y$$ Taking the logarithm on both sides: $$\log \left(\frac{b^2}{ac}\right)=\log x^y$$ Using the properties of logarithms: $$2\log b-\log a-\log c=y\log x$$ Substituting the values given in the problem statement: $$2q\log x-p\log x-r\log x=y\log x$$ Since $x\ne 1$, dividing each side by $\log x$ we get: $$y=\boxed{2q-p-r}$$