Answer:
18 workers should the landscaper bring to the job to finish a set of plants in 4 hours.
Explanation:
As given
Assuming that a set of plants can be installed in number of hours inversely related to the number of workers.
Let us assume that the number of hours needed for set up a plant be x.
Let us assume that the number of worker needed for setup a plant be y.
Thus


Where k is the constant of proportionality.
As given
A landscaper estimates that a set of plants can be installed in 6 hours by 12 workers.
x = 6 , y = 12
Thus


k = 72
As given
The landscaper wants to finish a set of plants in 4 hours.
x = 4 , k = 72
Thus


y = 18
Therefore 18 workers should the landscaper bring to the job to finish a set of plants in 4 hours.