So it is concluded that Xiaoming's mother's speed V2 = 20x3km/h = 60km/h.

As can be seen from the picture, Xiaoming didn't walk for half an hour, he was playing, so Xiaoming walked for 50 minutes, and Xiaoming's mother began to walk.

Therefore, the distance Xiao Ming walked: 20x50/60 km=50/3 km.

Let the time when Xiao Ming arrives at B be X, then the time from home to B for Xiao Ming's mother is (60x- 10) 60 h.

So there is: 50/3+20x=60X(60x- 10)60, and the solution is: x = 2/3 h.

Therefore, the total distance is: 60X(60X2/3- 10)X60=30km.