Then the return time is 75x/60 = 5x/4.

X+5x/4 = 36x = 16 (minutes)

Distance = 16 * 75 = 1200 (m)

Additional: look at the back first, and set the second bundle as X.

The first bundle is 7x/8.

Yes: 7x/8+8 = x-8.

X= 128

So the total is: 128+ 128 * 7/8 = 240.

Look at the front: level 6 accounts for 5/ 12.

Therefore, the number of seedlings of grade 6 = 240 * 5/ 12 = 100 (tree).

240- 100 = 140 is in grade four or five.

So the fourth level = 140 * 3/(3+4) = 60 (tree)

Grade 5 = 140-60 = 80 (trees)