Answer:
6 units
Step-by-step explanation:
You want the gravitational force between two objects after both the mass of one object and the distance between them triples, if it is initially 18 units.
Force
Let F represent the initial force between the objects. Newton's law of gravitational attraction tells us ...
F = GmM/r²
When one mass is tripled, and the distance between the objects is tripled, the new force is ...
F' = G(3m)M/(3r)² = 3/9(GmM/r²) = F/3
Given the initial force is 18 units, the new force of attraction is ...
F' = (18 units)/3 = 6 units
The new gravitational force of attraction between the objects is 6 units.