[กิตติ]

$z^3=8i \rightarrow \left|\,z\right|^3=8\rightarrow \left|\,z\right| =2 $
$\left|\,3 \overline{z}-2z^{-1}\right| =\left|\,\frac{3z\overline{z}-2}{z} \right| =\frac{ \left|\,3\left|\,z\right|^2-2\right| }{ \left|\,z\right|}$
$=\left|\,\frac{10}{2} \right| $
$=5$

ผมตอบ 4 ครับ