The distance traveled by the train is the length of the bridge plus the length of the train.

So the length of the truck is:

900× 3-2400 = 300m

2.

Push back. . .

On the fourth day, 1

On the third day, (1+ 1)*2=4.

The next day, (4+ 1)*2= 10.

The first day has (10+ 1)*2=22.

That is, my mother bought 22.

3.

A runs to the fourth floor and only needs to go to the third floor.

B run to the third floor, just go to the second floor.

So the speed ratio between Party A and Party B is 3: 2.

When A ran to the16th floor, he went to the15th floor.

B You can go to 15*2/3= 10.

Run to the floor of10+1=11