Final answer:
Doubling the mass of one object in a gravitational system doubles the gravitational force between the two objects, resulting in a new force of 36.0 N.
Step-by-step explanation:
If the mass of one of the objects in a two-object gravitational system is doubled, the gravitational force between the two objects will also double. According to Newton's law of universal gravitation, the force of gravity is directly proportional to the product of the two masses and inversely proportional to the square of the distance between their centers. Therefore, if one mass is doubled, the gravitational force will increase to 36.0 N, assuming the distance remains constant.