Solution: Suppose the departure time from the train is x hours.

15min =1/4h,10min =1/6h.

50(x- 1/4)=40(x+ 1/4)

Solution: x=2.25

The distance from the Xu family to the railway station = 50× (2.25-1/4) =100 (km).

So: vehicle speed100 ÷ (2.25-1/6) = 48 (km/h).