Let the distance from point A to Beishan Station be X, and the time for the car to drive to point A be Y..

60*y= 18-x

(60-4)*y/(60+4)+y=x/4

(Time when Group B meets the car+Walking time when Group B starts = Walking time after Group A)

x=2

y=4/ 15

The distance from point A to Beishan Station is 2 kilometers.