Solution: 0.8x+ 1.2x-8.4=0.

2x=8.4

x=4.2

② The distance between two sides is the height and length of both sides.

Short side length: 24 ÷ 4 = 6m Long side length: 24 ÷ 3 = 8m.

(3) A steel plant produces 22 1 ton of steel every day in the first three days of the week, and 987.5 tons in the last four days. How many tons are produced on average every day?

(22 1×3+987.5)÷(3+4)≈236 (ton)

An express train and a local train are going in opposite directions. The express train is 280 meters long and the local train is 385 meters long. The time for people sitting on the express train to see the local train pass is 1 1 sec. How long will it take people sitting in the local train to see the express train pass by?

According to the meaning of the question, the sum of the speeds of the two cars =385÷ 1 1=35m/s (meters per second).

Because the local train is 280 meters long.

So the time for people sitting on the local train to see the express train pass is 280÷35=8 seconds.