(x-60)*3= 120

X= 100 km/h

(2) The express train and the truck leave from A at the same time, and when they arrive at A, the express train arrives at the destination.

Distance between A and B: 100*3=300 kilometers.

(3) It takes 45 minutes * * * for the express truck to load the goods after loading the goods. The truck continues to move to point B, and the express truck starts to set off.

Distance between two cars: 120-60 * 3/4 = 75km.

B( 15/4，75)

(4) Let the speed of the express train from B to A be X.

75/(x+60)= 17/4- 15/4 = 1/2

X = 90km km/h