When time t=0 hours, the distance between the two cars is 900km, which means that the distance between Party A and Party B is 900 km.
2. When the local train is driving for 4 hours, the distance between the two cars is 0, indicating that the two cars meet;
3. When the local train travels 10 hour, the local train travels 900km, that is, the local train reaches the first place;
In this way, the speed of the local train can be calculated as: 900÷ 10=90 (km/h).
Let the express train speed be xkm/ h, then 4x+90x4=900, and the solution is: x= 135.
Answer; The speed of the express train is135 km/h.