Suppose: the teacher takes one student to walk X kilometers and the other student to walk. After the teacher put down the first student, the student went to the finish line, and the teacher returned to pick up another student, and then set off for the finish line together.

The teacher put the student down and another student left: 5*(x/20)=x/4 km.

Then the time for the teacher to return to meet the students =3x/4/(5+25)=x/40 hours.

In this way, the distance from the finish line is = 33-x/4-5 * x/40 = 33-x/4-x/8 = 33-3x/8km.

At this time, the distance from the first student to the finish line =33-x-5*x/40=33-9x/8 km.

If they arrive at the same time, the equation

(33-3x/8)/20=(33-9x/8)/5

33-3x/8=4*(33-9x/8)

33x/8=3*33

X=24 kilometers

The last period of time is: (33-3 * 24/8)/20 = (33-9)/20 =1.2 hours.

Then the total time = 24/20+24/40+1.2 =1.2+0.6+1.2 = 3 hours, which meets the conditions.

So the plan is as follows: the teacher takes one student to ride a motorcycle and the other student walks at the same time. After walking 24km, the teacher put down the first student, the first student began to walk to the finish line, the teacher returned to pick up another student, and then set off for the finish line together.