If the radius of the second Bohr orbit of a singly ionized helium...

The radius of the $n$-th Bohr orbit for a hydrogen-like species is given by $r_n \propto \dfrac{n^2}{Z}$.

For the second Bohr orbit of $He^+$ ($n = 2$, $Z = 2$):
$x \propto \dfrac{2^2}{2} \Rightarrow x \propto 2$

For the third Bohr orbit of $Li^{2+}$ ($n = 3$, $Z = 3$):
$r \propto \dfrac{3^2}{3} \Rightarrow r \propto 3$

Taking the ratio of the two radii:
$\dfrac{r}{x} = \dfrac{3}{2}$

$r = \dfrac{3}{2}x$

Answer: $\dfrac{3}{2}x$