8. Car A and Car B start from locations $A$ and $B$ respectively at the same time, heading towards each other. They meet after 3 hours, then Car A turns around and heads back to $\mathrm{A}$, while Car B continues on. After Car A reaches $A$ and turns around to head towards $B$, it meets Car B again half an hour later. Therefore, the total time for Car B to travel from $A$ to $B$ is $\qquad$ hours.
$7.2$