60X+50=80X

The solution is X=2.5.

2。 125 people, every 5 people 1 line, that is, 5 lines. If the interval between rows is 2 meters, then the team is 20 meters long.

T=(32+40)/40= 1.8 minutes

3。 Let hydrogen be x and oxygen be 8X.

X+8X=5.4

X=0.6，

8X=4.8

4。 If the speed of the express train is 3 times, then the local train is 2 times.

3×3.5+2×3.5 = 350

X=2

So the express 3X=6 and the local 2X=4.