2(20-x)=4

The solution is x= 18.

Answer: B train speed 18km.

2. let the speed of b be x.

2(a-x)=0.4

The solution is x=a-0.2.

Answer: The speed of train B is a-0.2 kilometers per hour.

3.( 1) Meet x hours after departure.

(60+80)x=448

The solution is x=3.2.

Answer: meet 3.2 hours after departure.

(2) X hours after the express train leaves, two cars meet.

60×28/60+(60+80)x=448

The solution is x=3.

Attendant: The express train leaves for three hours and the two trains meet.

(3) X hours after the departure, the express train will catch up with the local train.

448+60x=80x

The solution is x=22.4.

A: The express train caught up with the local train 22.4 hours after its departure.

4.8 people have X cars and 4 people have Y cars.

8x+4y=36

When x= 1 and y=7, 300+200×7= 1700 yuan is needed.

When x=2 and y=5, it needs 300×2+200×5= 1600 yuan.

When x=3, y=3. At this time, it needs 300×3+3×200= 1500 yuan.

The minimum car rental scheme is: 8 people with 3 cars and 4 people with 3 cars.

5. First purchase of Class A (70- 14)÷2=28kg.

I bought 70-28 = 42 kg for the second time.

Class a expenses are 28×3+42×2.5= 189 yuan.

For class B: 70×2= 140 yuan.

Then the overtime pay is more than that of Class B. 189- 140=49 yuan.