= Solution
For inner radius $a$ and outer conductor's inner radius $b$, <Gauss's law> gives $E(s)=\lambda/(2\pi\epsilon_0\epsilon_rs)$. Integrating across the <dielectric> gives <voltage> $V=\lambda\ln(b/a)/(2\pi\epsilon_0\epsilon_r)$. Thus the <capacitance> per unit length is
$$
\boxed{C'=\frac{2\pi\epsilon_0\epsilon_r}{\ln(b/a)}
=\frac{4\pi\epsilon_0}{\ln2}\simeq1.61\times10^{-10}\,\mathrm{F\,m^{-1}}
=161\,\mathrm{pF\,m^{-1}}.}
$$
The stated outer radius is interpreted as the radius of the dielectric-facing surface. <Magnetic permeability> affects <inductance>, but does not enter this electrostatic <capacitance>.
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