150 kg
The gravitational force between any two objects is affected by the masses of the objects and the distance between them. The greater the masses of the objects are, the stronger the gravitational force of attraction will be between those objects.
Since all four objects are the same distance from the star, only their masses affect the strength of the gravitational force. The object with a mass of 150 kg is the least massive, so this object is experiencing the weakest force of gravitational attraction toward the star.
