8. The speed of the yacht in still water is $x$ km/h, and the speed of the current is $y$ km/h. Pleasant Goat drives the yacht from downstream location $\mathrm{A}$ to upstream location $\mathrm{B}$, and then immediately returns to downstream $\mathrm{A}$. The time it takes for the yacht to travel from $\mathrm{A}$ to $\mathrm{B}$ is twice the time it takes to travel from $\mathrm{B}$ to $\mathrm{A}$. Therefore, $\frac{x}{y}=$ $\qquad$ .