Solution: the speed is 60 km/h and the driving distance is:

4.5x60 = 270km

Assume that the estimated time after deceleration is x km/h.

40(x+0.5)=60x

x= 1

So the driving distance after deceleration is 40(x+0.5)=60 (km).

So the distance between Party A and Party B is 270+60=3 10 (km).