(2) According to the image, the speed of Class A is 4km/h and that of Class B is 5km/h,

4x+5x= 10，

The solution is x= 10/9 h,

When x= 10/9 and y =-5×10/9+10 = 40/9,

When they met, Class B was 40/9 kilometers from the ground.

(3) Class A and Class B are four kilometers apart for the first time.

In other words, the sum of the distances traveled by the two categories is 6km.

So 4x+5x=6,

The solution is x = 2/3h.

It takes 2/3 hours for Class A and Class B to be 4 kilometers apart for the first time.

or

Answer: (1) y 1 = 4x (0 ≤ x ≤ 2.5), y2 =-5x+ 10 (0 ≤ x ≤ 2).

(2) According to the meaning of the question, when the two classes meet, the distance between A and B is equal, that is, y 1=y2, from which a linear equation can be obtained.

-5x+ 10=4x，

Solve this equation and get x= (hours).

When x=, y2 =-5×+ 10 = (km).

(3) According to the meaning, y2 -y 1=4.

That is -5x+ 10-4x=4.

Solve this equation and get x= (hours).

A: It takes several hours for Class A and Class B to be separated by 4 kilometers for the first time.