h.

18 minutes =0.3 hours

( 12-8)x =( 12+8)(0.3-x)

Solution: x=0.25

So: (12-8)x= 1.

A: The queue length is 1 km.

Analysis: The whole process can be divided into two parts:

1. The correspondent arrives at the front of the line (belonging to the problem of chasing in the same direction at the same time)

Team length at this time: (12-8)x

2. The correspondent returns to the end of the line (belonging to the encounter problem of walking in the opposite direction at the same time)

Team length at this time: (12+8)(0.3-x)

Because the lines are the same.

Therefore, the equation can be listed to find the queue length.