9. Given that two cars, A and B, start from points $A$ and $B$ respectively at the same time, and travel back and forth between $A$ and $B$ at a constant speed. If after the first meeting, car A continues to drive for 4 hours to reach $B$, while car B only drives for 1 hour to reach $A$, then when the two cars meet for the 15th time (excluding meetings at points $A$ and $B$), they have driven $\qquad$ hours.
$86$