The number of willows that can be planted =99/9+ 1= 12 (tree)

Number of Sophora japonica trees that can be planted =12-1=11(plant)

The distance between every two Sophora japonica trees = 9m.

Suppose the road is 9 meters long and willows are planted at both ends, that is, two willows are planted. Two willows were intercropped with 1 locust tree, so 1 locust tree was planted. Now the road is extended by 9 meters, which is 18 meters: then * * * will plant 3 willow trees and 2 locust trees, the first locust tree is 4.5 meters away from the second willow tree, and the second locust tree is 4.5 meters away from the second willow tree, which adds up to 9 meters, which means the distance between the two locust trees is 9 meters. And so on until the road is 99 meters long:

The number of willows that can be planted =99/9+ 1= 12 (tree)

Number of Sophora japonica trees that can be planted =12-1=11(plant)

The distance between every two Sophora japonica trees = 9m.