84. As shown in the figure, a truck travels from $A$ to $C$ at a speed of 50 km/h. At the same time, two couriers, Jia and Yi, start from $B$ and head towards $A$ and $C$ respectively, and their speeds are the same. If Jia meets the truck after traveling 3 km, and 12 minutes later, the truck and Yi arrive at $C$ simultaneously. Then the distance between $A$ and $C$ is 
$\mathrm{A}$ truck
Jia
B $\qquad$
$\qquad$ km. $\qquad$
Reference answer: 17.5
Key point: Travel problem - multiple people meeting and chasing