Self-Inductance

A circuit consists of a long thin conducting shell of radius $a$ and a parallel return wire of radius $b$ on axis inside. If the current is assumed distributed uniformly throughout the cross section of the wire, calculate the self-inductance ( $L$ ) per unit length. If you answer comes in the form

$\frac Ll=\frac{\mu_0}{\alpha \pi}\left(\frac{\mu_r}\beta + \log\frac{a^\gamma}{b^\delta}\right)$

Type your answer as $\alpha+\beta+\gamma+\delta=?$