smc

To get from the second term to the fourth term, we add $2$ lots of the common difference, so if the common difference is $d$, we have $2d=2x-x=x⟹d=\frac{x}{2}$. Thus the sequence is $\frac{x}{2},x,\frac{3x}{2},2x$, so the ratio is $\frac{\frac{x}{2}}{\frac{3x}{2}}=\frac{1}{3}$, which is answer $\boxed{\frac{1}{3}}$.